NETCONF WG R. Mahy
Internet-Draft Plantronics
Intended status: Informational S. Chisholm
Expires: September 11, 2008 Nortel
L. Lhotka
CESNET
March 10, 2008
Defining Netconf Data Models using Document Schema Definition Languages
(DSDL)
draft-mahy-canmod-dsdl-01.txt
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Copyright (C) The IETF Trust (2008).
Abstract
This document describes a concrete proposal for creating Netconf and
other IETF data models using the RelaxNG schema language and the
Schematron validation language, which are both part of ISO's Document
Schema Definition Languages (DSDL) standard.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3. RelaxNG . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4. Processing annotations for additional validation . . . . . . . 8
4.1. The 'unique' annotation . . . . . . . . . . . . . . . . . 8
4.2. The 'key' annotation . . . . . . . . . . . . . . . . . . . 10
4.3. The 'keyref' annotation . . . . . . . . . . . . . . . . . 11
4.4. The 'mustUse' annotation . . . . . . . . . . . . . . . . . 13
4.5. The 'infoType' annotation . . . . . . . . . . . . . . . . 13
4.6. Additional validation rules . . . . . . . . . . . . . . . 14
5. Validating instance data automatically with Schematron . . . . 15
5.1. Schematron patterns for data model validation . . . . . . 16
5.2. Phases of validation . . . . . . . . . . . . . . . . . . . 17
6. Validating the data model itself . . . . . . . . . . . . . . . 18
7. Documentation annotations . . . . . . . . . . . . . . . . . . 19
7.1. Creator information . . . . . . . . . . . . . . . . . . . 19
7.2. Descriptions, defaults, and units . . . . . . . . . . . . 19
7.3. Semantic Hints . . . . . . . . . . . . . . . . . . . . . . 20
8. Extensibility Model . . . . . . . . . . . . . . . . . . . . . 22
8.1. Pattern scoping using modules . . . . . . . . . . . . . . 22
8.2. Extending existing modules (forward compatibility) . . . . 23
8.3. Backwards Compatibility . . . . . . . . . . . . . . . . . 24
8.4. Default Values . . . . . . . . . . . . . . . . . . . . . . 24
9. Netconf Specifics . . . . . . . . . . . . . . . . . . . . . . 26
9.1. Get and Get-config operations . . . . . . . . . . . . . . 26
9.2. Edit-config operations . . . . . . . . . . . . . . . . . . 26
9.3. Netconf notifications . . . . . . . . . . . . . . . . . . 27
9.4. New netconf actions . . . . . . . . . . . . . . . . . . . 28
9.5. Netconf specific error messages . . . . . . . . . . . . . 29
9.6. Scope of an XML document . . . . . . . . . . . . . . . . . 31
10. Conformance . . . . . . . . . . . . . . . . . . . . . . . . . 32
10.1. Cardinality . . . . . . . . . . . . . . . . . . . . . . . 33
10.2. Operations on managed objects . . . . . . . . . . . . . . 33
10.3. Element and Attribute Status . . . . . . . . . . . . . . . 34
10.4. Additional Conformance Information . . . . . . . . . . . . 35
10.5. Schema Level Conformance - Server-side . . . . . . . . . . 35
10.6. Schema Level Conformance - Client-side . . . . . . . . . . 35
11. Grading against the requirements . . . . . . . . . . . . . . . 35
11.1. Met requirements . . . . . . . . . . . . . . . . . . . . . 35
11.2. Met applicable subset . . . . . . . . . . . . . . . . . . 42
11.3. Not Met . . . . . . . . . . . . . . . . . . . . . . . . . 43
12. Full Examples . . . . . . . . . . . . . . . . . . . . . . . . 44
13. "DML" Annotations Schema . . . . . . . . . . . . . . . . . . . 49
14. Security Considerations . . . . . . . . . . . . . . . . . . . 51
15. IANA Consideration . . . . . . . . . . . . . . . . . . . . . . 51
16. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 51
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Appendix A. XSLT Transform from processing annotation to
Schematron . . . . . . . . . . . . . . . . . . . . . 52
Appendix B. Schematron for validating data model documents . . . 52
Appendix C. Data type library . . . . . . . . . . . . . . . . . . 52
C.1. About Domain-Specific Pattern Libraries . . . . . . . . . 53
C.1.1. Internet Data Types . . . . . . . . . . . . . . . . . 54
C.1.2. IEEE Data Types . . . . . . . . . . . . . . . . . . . 58
Appendix D. DHCP schema in Relax XML format . . . . . . . . . . . 59
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 64
17.1. Normative References . . . . . . . . . . . . . . . . . . . 64
17.2. Informational References . . . . . . . . . . . . . . . . . 65
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 66
Intellectual Property and Copyright Statements . . . . . . . . . . 67
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1. Introduction
The NETCONF Working Group has completed a base protocol [1] used for
configuration management. This base specification defines protocol
bindings and an XML [5] container syntax for configuration and
management operations, but does not include a modeling language or
accompanying rules for how to model configuration and status
information (in XML syntax) carried by Netconf. The IETF Operations
area has a long tradition of defining data for SNMP [14] Management
Information Bases (MIBs) using the SMI [15] to model its data. While
this specific modeling approach has a number of well-understood
problems, most of the data modeling features provided by SMI are
still considered extremely important. Simply modeling the valid
syntax rather than additional semantic relationships has caused
significant interoperability problems in the past. The Netconf
community concluded that a data modeling framework is needed to
support ongoing development of IETF and vendor-defined management
information modules.
A design team collected, clarified and categorized requirements [13]
for a data modeling language from a broad group of IETF participants.
Many of these requirements have broad agreement within the design
team. This document describes an approach that addresses all the
broadly agreed requirements and the vast majority of the additional
requirements.
The approach to data modeling described here uses the two most mature
parts of the ISO Document Schema Definition Languages (DSDL) [26]
multi-part standard: Relax NG and Schematron (see also Part 1 of DSDL
- the overview [17] and an overview presentation on DSDL [27]). The
proposal then goes on to define additional processing and
documentation annotation schema. Relax NG [9] is a mature,
traditional schema language for validating the structure of an XML
document. Schematron [8] is a rule-based schema validation language
which uses XPath [10] expressions to validate content and relational
constraints. In addition, this document defines and reuses various
annotation schema which can provide additional metadata about
specific elements in the data model such as textual descriptions,
default values, relational integrity key definitions, and whether
data is configuration or status data.
This combination was created to specifically address a set of
Netconf-specific modeling requirements, and in addition should be
useful as a general purpose data modeling solution useful for other
IETF working groups. The authors believe that reusing schema work
being developed and used by other standards bodies provides
substantial long-term benefits to the IETF management community, so
this proposal attempts to reuse as much existing work as possible.
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2. Overview
This document proposes a concrete data modeling environment which
meets the Netconf data modeling design team requirements but is
otherwise very general purpose in nature. The proposal is quite
modular and draws from a number of existing standards and well-
understood schemas. Relevant requirements will be mentioned in each
major section, but a table of requirements is included in Section 11.
In order to make it easier to compare various proposed solutions to
provide a framework to define NETCONF content, each proposal produced
a non-trivial data model description to generate an instance document
compatible with the DHCP configuration example document in Appendix C
of the requirements document. The full example data model document
is shown in Section 12.
This document starts in Section 3 by describing the use of RelaxNG to
model XML syntax, element and attribute names, containment
relationships, cardinality, data types, and simple range and pattern
restrictions. RelaxNG can use its own basic type definitions or
reuse the W3C XML Schema Datatypes [6] definitions. It is also
straightforward to reference one or more external libraries of data
types, such as the IP and IEEE networking type libraries defined in
Appendix C.
While using an existing schema language is a good start toward the
data modeling requirements, a data modeling solution also needs
additional semantics conveyed. Section 4 describes "processing
annotations" which describe validation rules for instance documents
based on the data model. These annotations are incorporated inline
with the RelaxNG schema. Most of these validation rules can be
validated either in source code generated by a human or in a machine
readable way. The machine readable rules make extensive use of XPath
[10] expressions. [TODO: illustration here] An XSLT [11] (Extensible
Stylesheet Language: Transformations) document described in
Appendix A can convert the machine readable rules in a specific data
model document into a Schematron validation document for that data
model. This conversion is done only once each time the data model is
modified.
Section 5 describes how a Schematron document is used to validate an
instance document, and describes a set of three different levels or
phases of validation that this proposal supports. Section 6
describes how Schematron can validate a very different set of rules
on data model documents to make sure that they comply with specific
conventions. This document defines a set of Schematron rules in
Appendix B, which are compatible with content restrictions imposed by
Netconf.
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Section 7 describes how to attach document metadata (ex: title,
author, dates), per element descriptions, semantic hints about
elements, default values, units, and conformance status (active,
deprecated, obsolete) to the data model as documentation annotations.
Most of the document metadata is described using the Dublin Core [2]
metadata schemas. Default values are described using the DTD
(Document Type Definition) compatibility annotations [28]. The
definition for units is copied from the units definitions used by the
Geographic Markup Language GML [19]. The rest of these annotations
are defined in a RelaxNG annotation schema in Section 13.
Section 8 describes the extensibility and versioning model envisioned
by this proposal. It also describes the interaction between default
values and extensibility in this proposal.
Finally, Section 9 describes how to use the data model to support
Netconf-specific requirements. In particular, this section describes
how to model Netconf notifications [4] of a nearly full DHCP scope
and an IP address conflict, a Netconf-specific error response, and
the definition of a new action to revoke a lease.
3. RelaxNG
RelaxNG is an XML schema language developed by OASIS [29] and then
adopted by ISO as Part 2 of DSDL. It is now a full ISO standard.
RelaxNG has a reputation that it is easy to read and easy to learn.
RelaxNG has a solid theoretical basis, and is the canonical schema
format for several major W3C standards (XHTML [20], SVG [21], XML
signature [22], RDF [23]). RelaxNG includes strong support for XML
namespaces [7], treats attributes and elements similarly, and can
define schemas which support (or do not support) unordered content.
It can use integral types or an external data type library such as
W3C XML Schema Datatypes.
Unlike W3C XML Schema [24] (referred to later as XSD or WXS), RelaxNG
only describes the structure and contents of XML documents. RelaxNG
intentionally does not try to modify the information set of an XML
document. For example, it does not address default values (supported
in XML Data Type Definitions) or key and keyref types (supported in
W3C XML Schema). Since RelaxNG supports arbitrary annotations, other
languages can add semantics to a RelaxNG schema. Indeed, the RelaxNG
DTD compatibility schema includes annotations for default values.
The rest of DSDL also follows this modular philosophy. Part 6 of
DSDL (work not started) is reserved for path-based integrity
constraints (analogous to XSD keys and keyrefs).
RelaxNG has both an XML representation and a Compact representation.
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They can be converted automatically using open source tools such as
Trang [30]. Trang can also convert either form of RelaxNG to XSD
format automatically with some minor restrictions (RelaxNG can
represent some schema which XSD cannot). This document will use the
Compact form for brevity and readability throughout.
In RelaxNG Compact syntax, the symbols '?' (one or zero), '+' (one or
more), and '*' (zero or more) have their familiar meaning. The
symbol ',' indicates the next pattern follows in order, the symbol
'&' indicates that the next element can come before or after the
current pattern, and the '|' symbol indicates a choice among
patterns. Below is an example of a RelaxNG Compact schema snippet,
simplified from the schema for the full example in this proposal.
start = element-dhcp
element-dhcp = element dhcp {
element subnet {
element network { ipv4-address-content },
element prefix-length {
xsd:short { minInclusive = "0" maxInclusive = "32" }
}
element-range?,
element leases {
element-lease*
}?,
}*
}
element-range = element range {
element low { ipv4-address-content },
element high { ipv4-address-content }
}
element-lease = element lease {
attribute ip-address { ipv4-address-content },
element starts { xsd:dateTime },
element ends { xsd:dateTime },
element mac-address { mac-address-content }
}
A full tutorial on RelaxNG [31] is beyond the scope of this document.
This proposal will try to introduce unfamiliar concepts as they
appear, but in some cases, the reader may wish to consult an outside
reference or tutorial. More information on RelaxNG is available in
relaxng book [16] and at the following web sites:
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4. Processing annotations for additional validation
RelaxNG readily accepts annotations in other namespaces. For
example, one of the RelaxNG DTD compatibility annotations is used to
specify descriptive text about the element (shown as an initial
annotation); another compatibilty annotation specifies default values
(shown as a following annotation):
namespace compat = "http://relaxng.org/ns/compatibility/annotations/1.0"
element ice-cream {
[
compat:documentation ["Defines two flavors or ice cream"]
]
("vanilla" | "chocolate") >> compat:defaultValue ["chocolate"]
}
or in Relax NG XML format:
Defines two flavors of ice cream
vanilla
chocolate
chocolate
There are a variety of reasons to add annotations, but this section
of the proposal focuses on annotations which can be used to define
further processing on an instance document, especially validation.
Processing annotations could be implemented automatically by a
machine or by a human reading descriptive text in the data model who
implements source code. This document defines a new schema for both
processing annotations and documentation annotations. This section
begins by explaining the semantics of each of the processing
annotations defined here. In our examples, this annotation schema
will use the namespace prefix 'dml'.
4.1. The 'unique' annotation
The 'unique' annotation element specifies an expression (usually an
element) that needs to be unique within a list. The annotation can
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follows any element definition which has a cardinality greater than
one ('+' or '*'). The content of the unique element is an XPath [10]
expression which is evaluated relative to the element it follows (and
its immediate parent). For example, in the following example, the
'port' element has to be unique within all other service elements
under the servers element:
element-servers = element servers {
element service {
element name { xsd:string },
element port { xsd:unsignedShort }
>> dml:unique ["port"]
}+
}
# '//servers/service' must have only one 'port' with a specific value.
In terms of XPath expressions, this means that in the context
'//servers/service/port', the XPath expression 'count( //servers/
service[port=current()] ) = 1' needs to be true. (Does the number of
service elements with a port element equal to the value of the
current port element equal 1?). Expressing this rule as a series of
XPath expressions makes the rule more precise, but it also enables a
conversion of this constraint to a Schematron validation rule as
discussed in Section 5. In the following snippet of instance
document, the second http service is not allowed since its port
number conflicts with another service.
ssh
2222
http
80
http
2222
This syntax is also capable of specifying that the combination of one
or more fields is required to be unique.
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4.2. The 'key' annotation
In many cases, something is unique in a list because it is actually a
key used in cross-element relationships. The 'key' annotation
specifies that an expression can be used as a unique lookup key among
the elements of a list (an element with cardinality greater than
one). In addition, this key can be used in another element which is
a key reference (keyref) to provide referential integrity between
these related elements. As with the 'unique' element, the content of
the 'key' element is an XPath expression which is evaluated relative
to the element it follows (and its immediate parent).
As shown in the next example, the key can be a compound key (formed
from more than one element or attribute), and it can reference
descendants of arbitrary depth to form the key. The key to the
subnet element in the instance document is "192.168.24.0/24".
Keys are critical for any data that will be configured or for any
data that will be referenced via a keyref statement. Therefore key
definitions are mandatory for all lists except as described below.
For convenience, some lists have an implicit key:
o list elements which have an 'id' (key) attribute with the type
xsd:ID;
o list elements which have only an 'xml:lang' (key) attribute and
only contain character data (no subelements);
o list elements which have no character data and a single mandatory
(key) attribute; and
o list elements which contain only character data (no subelements)
and which have no attributes (the character data is the key).
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element-dhcp = element dhcp {
element subnet {
element prefix {
element network { ipv4-address-content },
element prefix-length {
xsd:short { minInclusive = "0" maxInclusive = "32" }
}
},
element-range
>> dml:key ["concat(prefix/network, '/', prefix/prefix-length)"]
}+
}
192.168.24.0
24
192.168.24.20
192.168.24.250
The validation rule for keys are as follows: If an XML element with a
maximum cardinality greater than one (for brevity a 'list element')
has an 'id' attribute with type 'ID', the validation rules defined
here will use the 'id' attribute as the list key. If a list element
consists only of a single text value and no attributes, the
validation rules defined here will use the text value as the key
unless a different key definition is explicitly provided. Likewise,
if a list element consists of an empty value and has only one
attribute, the attribute will be used as the key unless a different
key definition is explicitly provided.
4.3. The 'keyref' annotation
The contents of the 'keyref' annotation contains an XPath expression
which points to the element under which a 'key' annotation was
defined. In the example in the previous section, the key element
annotates the 'subnet' element. Therefore a keyref annotation
referring to a specific subnet element will use the XPath expression
'//dhcp:subnet'. Note that keyrefs could often refer to elements in
a different namespace. For example, in the example that follows, the
dhcp:interfaces-filter element consists of a list of tokens which
refer to keys defined under the //int:interface schema definition.
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element-subnet = element subnet {
element network { ipv4-address-content },
element prefix-length {
xsd:short { minInclusive = "0" maxInclusive = "32" }
},
element interface-filter {
element interface {
xsd:token
>> dml:keyref ["//int:interface"]
}+
}
}
element-interfaces = element int:interfaces {
element int:interface {
element int:ifIndex { xsd:token },
element int:ifType { xsd:token }
>> dml:key ["int:ifIndex"]
}+
}
10.1.1.0
24
lo0
en2
lo0
en1
en2
Be aware that in some cases, a list may consist of elements which
have both a key and keyref (a list of keyrefs).
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4.4. The 'mustUse' annotation
An element in the data model tagged with the 'mustUse' annotation
indicates that the tagged element needs to appear in the instance
document whenever its parent appears. Items with a defaultValue
annotation cannot also have a mustUse annotation.
In many schemas, there is a facility for using fragments or
patches of XML documents. (Netconf uses these fragments
extensively in edit-config operations for example). In order to
accommodate these fragments, the cardinality of an otherwise
"required" element may allow the element to be optional in an XML
fragment. The mustUse annotation provides a way to express what
is actually required in this situation.
See also the client-side conformance discussion in Section 10.
4.5. The 'infoType' annotation
The 'infoType' annotation indicates the category of data that applies
to the annotated element and all its children until another
'infoType' annotation. The content of the 'infoType' element is an
enumeration. The 'config' type is the default value. It indicates
that the covered data is configuration and that it is at least
theoretically possible to include this data in read, write, create,
and delete operations. Likewise 'status' and 'statistics'
information can be read, but cannot be included in write, create, and
delete operations.
The example below indicates that the 'leases' element and all its
sub-elements are status information and not suitable for creating,
writing, or deleting.
element-leases = element leases {
element lease {
attribute ip-address { ipv4-address-content },
element starts { xsd:dateTime },
element ends { xsd:dateTime },
element mac-address { mac-address-content }
}*
>> dml:infoType ["status"]
}
In addition, this annotation element has optional minAccess and
maxAccess attributes which can override the default list of relevant
operations. These attributes are discussed in more detail in
Section 10.
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Finally, the infoType is used to describe which elements are part of
a notification or other action, for example as used in Section 9.3
and Section 9.4 respectively.
4.6. Additional validation rules
In our DHCP example, the validation statement that "subnets can't
overlap" is easy to say in English, but hard to write formally. In
addition, some validation tests may be difficult or impossible to
evaluate without local state information. The 'manual-validation-
rule' annotation provides a natural language explanation of a
validation constraint that can only be evaluated by a human. When
validation rules (as in Section 5) are automatically generated, a
warning will be generated for each manual-validation-rule.
element-subnet = element subnet {
element network { ipv4-address-content },
element prefix-length {
xsd:short { minInclusive = "0" maxInclusive = "32" }
}
>> dml:manual-validation-rule [xml:lang="en"
"Subnets may not overlap"]
>> dml:manual-validation-rule [xml:lang="fr"
"Les sous-reseaux ne peuvent pas se superposer"]
}
In addition, the data model can also define additional rules formally
by embedding specific Schematron rules. Schematron is a rule-based
validation language for XML documents. Schematron patterns define a
series of rules using XPath expressions which evaluate to a boolean
value. These rules contain human language text which could be used
to implement manual validation. The text node of the Schematron
assert statement should provide text suitable for a human to write an
equivalent validity check.
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element-dhcp = element dhcp {
[
sch:pattern [
sch:rule [
context = "//dhcp:dhcp"
sch:assert [
test = "dhcp:default-lease-time <= dhcp:max-lease-time"
"Default lease time cannot be larger than maximum lease time"
]
]
]
]
element default-lease-time { xsd:unsignedInt }?,
element max-lease-time { xsd:unsignedInt }?,
...
}
The preceding example consists of a single rule. In the context of
the 'dhcp' element, the value of the 'default-lease-time' element
needs to be less than or equal to the value of the 'max-lease-time'
element.
Both the 'dml:manual-validation-rule' and Schematron 'assert'
elements can contain an attribute to convey Netconf-specific error
messages. For more information, see Section 9.5.
Once these embedded Schematron rules are written, one vendor could
enforce these rules in code, while another could validate against the
embedded Schematron rules. A vendor can also use the provided XSLT
transformation in Appendix A to create a standalone Schematron file
from the data model.
5. Validating instance data automatically with Schematron
ISO Schematron is a rule-based validation language based on XPath
expressions. It is Part 3 of the DSDL standard. XPath is an
expression language for defining parts of an XML document; it uses
path expressions to navigate in XML documents and access XML nodes
(elements, attributes, text, namespaces, processing-intructions,
comments, and the root/document node. It also includes a library of
functions. The XSLT and XLink specifications also rely on XPath
expressions and built-in functions.
XPath uses path expressions to select nodes or node-sets in an XML
document. These path expressions look very much like the expressions
you see when you work with a traditional computer file system. While
a complete tutorial on Schematron [32] or tutorial on XPath [33] is
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beyond the scope of this document, we will walk through a simple
example to highlight the most important concepts. This example is
functionally the same as the example of Schematron embedded in
RelaxNG Compact in the last section. More Schematron resources are
available here:
5.1. Schematron patterns for data model validation
Below is a simple Schematron rule.
Default lease time cannot be larger than maximum lease time
The Schematron validator evaluates the context of each rule, then
evaluates each assert or report clause within the rule. Lets look at
a more complicated example that is used for insuring that a key is
unique within a list context.
The value ifIndex must be unique among all interfaces.
For every ifIndex element, the 'assert' tests if the number of
interfaces which have an ifIndex matching the current one (being
evaluated) is one. This XPath expression is rather long. Since we
will use this idiom repeatedly, we can define a Schematron abstract
pattern to express this more succinctly:
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The key "$key" needs to be unique within the list at: $context
Likewise, we can write Schematron abstract patterns for validating
keyref relationships as well.
The contents of "$keyref-context" must be a
with the key "$key" in this context: $key-context.
Even the Schematron abstract patterns shown above contain paths that
a computer could derive automatically. The XSLT stylesheet shown in
Appendix A reads the data model processing annotations to
automatically generate Schematron patterns that use these abstract
patterns. The XSLT stylesheet is just calculating the context XPaths
by examining the document structure in the RelaxNG schema. Once
generated, these rules can be used to test the validity of instance
documents. These Schematron tests can provide different levels of
validity checking.
5.2. Phases of validation
Conceptually, an implementation can validate its instance data in
different logical phases, adding more tests with each phase. We use
three levels or phases for validating an instance document. There is
a level of validation which is appropriate even for loose XML
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document fragments which still maintain their hierarchy (the fragment
phase), there is a level of validation appropriate for a cohesive XML
document but which may not be able to validate relational integrity
checks against some operational state (the standard phase), and there
is validation which includes all relational integrity checks (the
full validation phase). For example, in Netconf an edit-config
operation can cause the replacement a small fragment of XML. A
candidate configuration may be waiting for application but can't
check the readiness of a piece of hardware that the configuration
refers to.
From the NETCONF perspective, these three phrases can considered to
have the following scope and triggers:
1. the fragment phase: This can be run against individual NETCONF
operations; should be automatically triggered
2. the standard phase: This can be run against the candidate
configuration, but won't always pass; should be manually
triggered
3. the full validation phase: This can be run against a running
configuration; should be automatically triggered
During the Fragment phase validation:
o Verify that the content is appropriate to the operation (by
passing a variable to Schematron with the type of operation)
During Standard phase validation (all rules except for keyref
checking):
o Verify that mustUse items are present
o Check the uniqueness for unique and key annotations
o Print a warning if any manual validation rules are present
During Full phase validation: add keyref checks.
All embedded Schematron will run in the standard phase unless the a
'dml:phase' attribute is included with the name of a different phase
('fragment' or 'full').
6. Validating the data model itself
In addition to validating the instance data, it is necessary to
validate the data model document whenever the data model itself is
modified. In addition to syntax checks, the content of several of
the annotations can be validated. Finally, certain bindings or
usages will need to enforce constraints individual data model.
For example, Netconf needs the following restrictions:
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o Elements with cardinality greater than one (lists), which can have
more than one child element need to have a key defined.
o Mixed content (non-whitespace text nodes interleaved with
elements) is not allowed.
o All schema modules need to have a top-level version number
attribute.
The Schematron file in Appendix B will check these constraints.
7. Documentation annotations
This section describes annotations which do not have an effect on
validation.
7.1. Creator information
Metadata about the data model document (ex: title, author, dates) is
expressed using a combination of Dublin Core metadata terms, and the
DML schema defined in this document. This proposal recommends that
all data models include a Dublin Core title, creator, description,
and created (creation date) element. Data model authors can include
any additional Dublin Core metadata which is relevant. In addition,
the DML annotation schema adds an 'organization' annotation and a
'contact' annotation. Organization is a human readable string that
indicates the organization responsible for the data model. It
includes an optional language attribute. Contact is a URI that can
be used to reach the author or maintainer of the data model. Using a
mailto: URI is recommended. Finally, the version of the data model
is expressed in a 'dataModelVersion' annotation.
>> dc:title [ "Example schema for DHCP server" ]
>> dml:dataModelVersion ["1.0"]
>> dc:type ["Dataset"]
>> dc:creator [ "Rohan Mahy" ]
>> dml:organization [ "as an individual" ]
>> dml:contact [ "mailto:rohan@example.org" ]
>> dc:created [ "2008-02-13" ]
7.2. Descriptions, defaults, and units
Default values and semantic descriptions for individual schema items
use the RelaxNG DTD compatibility annotations.
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element default-lease-time {
xsd:unsignedInt
>> compat:defaultValue ["3600"] >> dml:units ["s"]
>> compat:documentation [ xml:lang="en"
"The default duration of a DHCP lease in seconds" ]
}?
Typically default values only apply to a specific version of a data
model. Default values which persist for all versions of a module are
identified with a special attribute as described in Section 8.4.
The 'units' annotation expresses the unit of measure for an element
with a numeric value. The syntax for this annotation is copied from
the GML (Geographic Markup Language) specification [19].
NOTE: It is recommended that the symbol be an identifier for a
unit of measure as specified in the Unified Code of Units of
Measure (UCUM) [12] (http://aurora.regenstrief.org/UCUM). This
provides a set of symbols and a grammar for constructing
identifiers for units of measure that are unique, and may be
easily entered with a keyboard supporting the limited character
set known as 7-bit ASCII. ISO 2955 formerly provided a
specification with this scope, but was withdrawn in 2001. UCUM
largely follows ISO 2955 with modifications to remove ambiguities
and other problems.
URL for GML specs is: http://www.opengeospatial.org/standards/gml
The compat:documentation annotation can also be used to provide
general descriptions of elements, similar to the DESCRIPTION tag in
SNMP MIBs.
7.3. Semantic Hints
Some schemas include container elements which have a semantic meaning
(for example, to enable a specific service) when they are present
even if they are empty. The 'existence' annotation provides a
semantic hint to a processor that such an element cannot be omitted
just because it is empty. (This document does not condone or condemn
this practice.)
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# snippet of data model
element-range = element range {
element low { ipv4-address-content }?,
element high { ipv4-address-content }?
>> dml:existence []
>> compat:documentation
["The presence of a range element turns on dynamic addressing " ~
"for the subnet. If low and high elements are missing, the " ~
"DHCP server serves dynamic addresses for the whole range " ~
"except for any router addresses on that subnet."]
}
10.254.240.0
22
The 'list-order' annotation conveys whether the order of a list is
semantically meaningful as another semantic hint. The value 'any-
order' means that order is not meaningful, while the value 'user-
order' means that the order of the elements in the list are
semantically meaningful. The default semantic in the absence of this
annotation is that order is not semantically meaningful.
element-router-list-option = element router-list {
element router { ipv4-address-content }+
>> dml:order ["user-order"]
}
The 'status' annotation is used to convey conformance status (active,
deprecated, obsolete) of a particular element. See Section 10 for
more detailed semantics of this annotation.
The data model can also include a 'mustUnderstand' annotation. This
annotation contains a space-separated list of namespace prefixes that
the consumer of the document must be able to understand to continue
processing the document. This attribute can also be included in
instance documents as described in Section 8.
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8. Extensibility Model
8.1. Pattern scoping using modules
This proposal expects large amounts of configuration will be split
into modules. A module represents a cohesive set of data about a
particular aspect of a device which is generally separable from other
aspects of the device. For example, configuration of a DHCP server
vs. a web server, or configuration of router interfaces vs. access
lists.
Each module needs to have its own namespace and a module version
number. Each module has a Relax NG start pattern indicating the top-
level element for that module. If this module is used as a
standalone document, the start pattern indicates the root element of
the XML document.
If (quite likely) a device supports several modules, a configuration
file can be constructed by including all the relevant modules as
external references. The entire grammar from the external reference
is included starting from the external start pattern. The patterns
in the external grammar are locally scoped so that a pattern in one
module does not conflict with another pattern of the same name in
another module. In the example below, the DHCP module and the
interfaces module both have an "element-interface" pattern, but this
does not cause a conflict since these patterns are in different
scopes.
# config-root.rnc
default namespace = "http://example.org/ns/root"
start = element-config
element-config = element config {
external "interfaces.rnc" ? &
external "dhcp.rnc" ?
}
The example above allows (and correctly validates) instance documents
with the following hierarchy:
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8.2. Extending existing modules (forward compatibility)
The authors envision that data model modules for Netconf and other
IETF protocols will have a small set of standardized modules and
potentially a much larger collection of vendor-defined modules.
Often standardized modules are partially open to allow vendors to
extend a data model without modifying the original core module
definition. Assume that the example DHCP module is a standardized
module and that a vendor wants to add two new extensions to this
module.
Rather than reference the standardized module directly in 'config-
root.rnc', the vendor creates a new module shim which includes the
core module and then either adds new definitions or includes
additional definitions. The shim can mix inline definitions with
included definitions.
# dhcp+extensions.rnc
include "dhcp.rnc" # base module
include "dhcp-tz.rnc" # timezone option extension
include "dhcp-wins.rnc" # WINS server option extension
The included files redefine an existing pattern in the base module by
combining the new content with the base content. Relax NG supports
combination through interleave (with the "&=" operator) and
combination through choice (with the "|=" operator). The example
here uses combination with interleave since the base module also used
interleave within the contents of 'element-dhcp-option'.
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# dhcp-tz.rnc
namespace tz = "http://example.org/ns/dhcp/timezone"
element-dhcp-option &= element tz:timezone { token }?
# dhcp-wins.rnc
namespace wins = "http://example.org/ns/dhcp/wins-option"
element-dhcp-option &= element wins:wins-server { token }*
8.3. Backwards Compatibility
All data models defined using this proposal are expected to have at
least one namespace URI per module and a top level dml:
dataModelVersion attribute which provides the current version number
for that module. The extensibility model suggested here has future
extensibility implications motivated strongly by the importance of
backwards compatibility.
Elements and attributes are never removed from the schema for a
particular namespace. However, content can be deprecated in any
version change. Content which was deprecated in a previous version
of the same schema can be made obsolete when updating the schema to
the next "major version number". Module maintainers can indicate the
status of module elements using the dml:status annotation.
In some cases the "no deletion" policy will cause content to migrate
to a new element name if the structure of the old element name was
poorly implemented. If the model developer truly wants to reuse an
element or attribute name which was made obsolete, the schema can
migrate to a new namespace.
It is not acceptable to add new mandatory content (content with
either a dml:mustUse annotation or content with a cardinality of at
least one) without breaking backwards compatibility. While this can
be a bit limiting when trying to add critical new features, adding
default values (see next section) to new optional content can get
around many of the limitations.
These limitation are not a result of using Relax NG, but rather
based on operational experience with SNMP, CLI and other
management interfaces. The goal is to provide stability to
NETCONF clients (operator scripts and management applications) and
other usages of this proposal using content defined using these
rules.
8.4. Default Values
There are a set of default values which are very stable over time and
across implementations. Typically these are related to a default or
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constant in a protocol. For example, the example below shows a timer
default defined in the SIP protocol [25]. This example adds an
attribute to the defaultValue annotation which indicates that this
particular default is a module-level default and will never change
for this element in this namespace:
element-sip-timers = element sip-timers {
element t1-timer {
xsd:positiveInteger
>> compat:defaultValue [ dml:moduleDefault="true"
"500" ] >> dml:units ["ms"]
}
...
}
These module defaults will be the same for all implementations of the
schema across different products and different versions.
Implementations themselves tend to have a set of default values which
differ from this module-level default. This second type, an
implementation default, differs between implementations and between
versions as appropriate. In fact, different implementations may have
different sets of elements for which they have defined default
values.
Implementation defaults are an important feature to be able to
maintain backwards compatibility. It allows for new elements to be
added to a schema in a way that clients not familiar with the new
elements can continue to send older configuration commands and still
successfully change the configuration in a deterministic and
predictable fashion. Given the static nature of module-level
defaults, they will rarely be used, so implementation defaults fill
this gap.
The proposal provides the ability for model developers to specify
default values when applicable. Whether these values are retrieved
as a result of various operations (ex: a 'get' or 'get-config'
operation in Netconf) is a protocol-specific behaviour and is not
prescribed by the solution. This provides the flexibility for the
protocol to support both an operation which returns elements who
currently have the default value and an operation which does not. It
also leaves it to the protocol to decide whether or not to present
elements who have been explicitly set to the same value as the
default.
When a compat:defaultValue annotation appears without the dml:
moduleDefault attribute, the defaultValue is an implementation (per-
version) default.
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9. Netconf Specifics
While many of the features described above are motivated by Netconf,
they all could be applicable or relevant to other data modeling
applications. The mechanisms described below are specific to
Netconf.
9.1. Get and Get-config operations
The get operation retrieves all data of any infoType. The get-config
operation only retreives data with an infoType of 'config'.
9.2. Edit-config operations
The edit-config operation can be performed on content whose
minAccess/maxAccess allows creation, modification or deletion and
which a particular implementation has provided supported for these
operations.
Creatable content are elements whose maxAccess clause allows creation
and that exist in an implementation that supports creation of that
element. Writable content are elements whose maxAccess clause allows
writing and that exist in an implementation that supports editing of
that element. Deletable content are elements whose maxAccess clause
allows deleting and that exist in an implementation that supports
deleting of that element. Readable content are elements whose
maxAccess clause allows reading and that exist in an implementation
that supports reading of that element.
During an edit-config operation using merge, if an element or
attribute is creatable and this object does not exist, it is created.
If it is not creatable, the an error is reported. During a replace,
If the element or attribute is writeable and exists, then all child
nodes not present in the XML that are deletable are deleted, and
child nodes present in the XML but not present in the datastore which
are creatable are created. During a create, the element or attribute
is created if it does not exist, if it is creatable. During a
delete, if the element or attribute is deletable the element is
deleted if it exists. An attempt to create, modify or delete
elements or child elements when these operations are not supported
will result in an error.
The copy-config operations replaces one configuration with another.
The access writes of the individual managed resources and data
elements involved in the configuration are not taken into account in
this case. The delete-config operation deletes an entire
configuration datastore. Likewise, the access writes of the
individual managed resources and data elements involved in the
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configuration are not taken into account.
Read-only data should not itself be included in an edit-config
operation, but may be included when an operation is performed on a
containing element with sufficient privileges. These elements get
created when their containing element is created and deleted when
their containing element is deleted.
9.3. Netconf notifications
Below is the definition of two Netconf notifications. The first
definition consists of completely new content. The second definition
contains new content and reuses a pattern from DHCP configuration
portion of the data model.
namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace xsd = "http://www/w3/org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace sch = "http://www.ascc.net/xml/schematron"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
namespace notif = "urn:ietf:params:xml:ns:netconf:notification:rng:1.0"
namespace ns1 = "notif"
default namespace = "http://www.example.com/dhcp"
compat:documentation [
"This schema demonstrates defining two Netconf notifications." ~
"The contents of the first notification is defined using" ~
"entirely new content. The second notification reuses content" ~
"defined for use in Netconf get operations."
]
include "notifications.rnc" inherit = ns1
notificationContent |=
[
compat:documentation [
"This notification is sent out when an IP address" ~
"conflict is detected. The DHCP client discovers" ~
"its assigned address is already in use."
]
]
element dhcpAddressConflictNotification {
element ip-address { ipv4-address-content },
element rogue-mac-address {
mac-address-content
>> compat:documentation ["The conflicting MAC address"]
},
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element leased-mac-address {
mac-address-content
>> compat:documentation ["The MAC address of the DHCP client"]
}
>> dml:infoType ["notify"]
}
notificationContent |=
[
compat:documentation [
"This notification is sent out when the dynamic" ~
"IP address range for a subnet is nearly full."
]
]
element dhcpScopeNearlyFullNotification {
(
element addresses-used { xsd:integer },
element addresses-avail { xsd:integer },
element-subnet
)+
>> dml:infoType ["notify"]
}
start |= notificationType
9.4. New netconf actions
Below is an example specification of a new Netconf action.
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namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace xsd = "http://www/w3/org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace sch = "http://www.ascc.net/xml/schematron"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
namespace netconf = "urn:ietf:params:xml:ns:netconf:base:1.0"
namespace ns1 = "netconf"
default namespace = "http://www.example.com/dhcp"
compat:documentation [
"This schema defines the dhcp revoke lease rpc action"
]
include "netconf.rnc" inherit = ns1
revokeLeaseType = element revoke-lease {
element address { ipv4-address-content }+
>> dml:infoType ["action"]
}
rpcType |= revokeLeaseType
start |= rpcType
9.5. Netconf specific error messages
Custom Netconf error messages are available as error annotation
attributes for Schematron. Schematron allows attributes from other
namespaces in all its elements. The 'dml:netconf-error-app-tag'
attribute can be used to provide a error-app-tag value specific to
the data model. In addition, the error text can be localized in
Schematron using the 'diagnostics' element.
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The contents of "$keyref-context" must be a
with the key "$key" in this context: $key-context.
The contents of "$keyref-context" must be a 'keyref'
with the key "$key" in this context: $key-context.
Les contenus de "$keyref-context" droite etre un 'keyref'
avec le cle "$key" dans cette contexte: $key-context
This would generate the following RPC error during an edit-config
with full validation enabled:
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application
invalid-value
error
keyref-failure
//dhcp:subnet[@key="192.168.16.0/24]
/dhcp:interface-filter[interface='en4']
The contents of "//dhcp:interface-filter" must be a 'keyref'
with the key "//int:ifIndex" in this context: int:interface.
Les contenus de "//dhcp:interface-filter" droite etre un 'keyref'
avec le cle "//int:ifIndex" dans cette contexte: int:interface
9.6. Scope of an XML document
All types of XML schemas validate based on the contents of a
"document". In the context of Netconf, what is considered a single
XML document for validation purposes is an important issue which is
directly related to the use of XML validation tools that can parse
Netconf data models. Three possibilities are worth considering:
o Each Netconf message is a document. Any XML inside the Netconf
message (both the "envelope" and the configuration or other
operational data) needs to be valid according to some combination
of schema.
o An entire device configuration is an XML document. In this case,
the schema included in a Netconf operation (especially in an edit-
config or get-config operation) is logically validated separately
from the Netconf "envelope". There can be mulitple documents
accessible to Netconf. For example, a device can support multiple
candidate configurations and a running configuration, each of
which is handled as a separate XML document. This option allows
individual configuration files on a disk to be validated.
o Each module is an XML document. This option is similar to the
second option, except that a naming convention for specific
instance files is needed for referential integrity validation to
succeed. Breaking a configuration file into smaller logical
chunks allows automatic validation to proceed more quickly and
consume less memory. It also insures that validation checks are
only run for configuration modules which have changed since the
last validation, or which refer to modules which have changed.
Another benefit of this approach is that it becomes much easier to
insure that non-random id attributes are unique within the scope
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of a document.
One of the implications of this choice is that the starting element
of an XML document needs to be specified, either in the schema
language (as supported in Relax NG) or externally in text and to
validators. This is an aspect of Netconf's usage of XML which is
underspecified and somewhat sloppy. The full DHCP configuration
example in Section 12 assumes option 2 and so it defines a root
config element (which would be required for option 2). However, each
module include a top level element which could become the root
element of its own document.
To implement option 3, the non-abstract Schematron rule described in
Section 5 for keyref validation would need to be modified slightly to
include the correct document name. Specifically, the key-context
would become something like: "document('interfaces.xml')//
int:interfaces/int:interface"
This proposal also used option 1 in order to demonstrate
notifications and actions which extend the Netconf protocol itself.
These example could be reworked to also include the relevant
configuration as an external reference to avoid naming conflicts.
Finally, part 4 of DSDL is the Namespace-based Validation Dispatching
Language (NVDL) could be useful for managing modules defined using
different schema languages. An NVDL script controls the dispatching
of elements or attributes in a given XML document to different
validators, depending on the namespaces of the elements or
attributes. An NVDL script also specifies which schemas are used by
these validators. These schemas can be written in any schema
language.
10. Conformance
When defining NETCONF content, it is also necessary to define
machine-readable conformance for that content. The conformance
method described provides a means of providing information about
individual elements which is then used to calculate the schema
conformance. There is no separate definition of schema conformance.
Previous solutions with separate conformance sections were found to
have issues, particularly in keeping them up to date as the schema
evolved. They also were not always used outside of standards
activities where people did not either fully understand them or see
the value in them.
Conformance specifies not only whether to object must be supported,
but also the level of access, read versus write for example that is
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minimally required.
10.1. Cardinality
When defining attributes and elements in the XML syntax, the
'optional', 'oneOrMore' or 'zeroOrMore' tags are used to specify the
cardinality of the element. In the compact syntax, "?" means
optional, "+" means one or more, "*" means zero or more. When no
cardinality indicator is present, this is interpreted to mean exactly
once.
10.2. Operations on managed objects
Operations that can be performed on managed objects fall into one of
the following equivalence classes: "create", "delete", "read",
"write", and "execute". A value of "create" means it is possible to
create new instances of this element. A value of "delete" means it
is possible to destroy instances of this element. A value of "read"
means that it is possible to view values of this element. A value of
"write" means it is possible to modify an instance of this element.
A value of "execute" means that there is a side effect execution such
as rebooting that is permissible as a result of the command.
The kind of access which is allowed for a particular element depends
on its infoType. The minimum access needed for an implementation for
a specific kind of infoType is that element's 'minAccess'. The
maximum access allowed is that element's 'maxAccess'. Normally these
values do not need to be modified. There is a default access class
for each infoType.
+---------------+-----------+--------------------------+
| Data Category | minAccess | maxAccess |
+---------------+-----------+--------------------------+
| config | read | read,write,create,delete |
| status | read | read |
| statistics | read | read,delete |
| action | execute | execute |
| notify | read | read |
+---------------+-----------+--------------------------+
Default access classes for infoTypes
However, if a specific piece of data needs a different class it can
be modified using the infoType annotation's minAccess and maxAccess
attributes. For example, perhaps a 'controller' element can only be
created automatically as a side-effect of some other action. The
example below documents this by explicitly setting the maxAccess
attribute:
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element-controller = element controller {
# a bunch of sub-elements of controller
# ...
>> dml:infoType [ maxAccess="read write delete" "config"]
>> compat:documentation ["Can't create a controller"]
}
To describe how this applies specifically to Netconf: a value of
"create" means it is possible to create new instances of this element
using commands like the NETCONF 'edit-config' or copy- config'
commands. A value of "delete" means it is possible to destroy
instances of this element using commands like the NETCONF 'edit-
config', 'copy-config' or 'delete-config' operations. A value of
"read" means that it is possible to view values of this element using
commands like the 'get-config', 'get' or 'notification' operations.
A value of "write" means it is possible to modify an instance of this
element using commands like the NETCONF 'edit-config' or 'copy-
config' commands. A value of "execute" means that there is a side
effect execution such as rebooting that is permissible as a result of
the command. For example, commands like the NETCONF 'edit-config' or
a 'copy-config' command or the ability to execute a commands like the
'lock', 'unlock' or 'kill-session' command.
10.3. Element and Attribute Status
As a schema evolves, certain elements and attributes may no longer be
relevant. Simply deleting these from the schema may be acceptable
for elements that did not see implementation, but others will require
a strategy to allow implementers to migrate away from the old
elements. An optional processing annotation called "status" SHOULD
be used to provide the status of the element. When not present, it
will assume a value of "current". The other value of this object are
"deprecated" and "obsolete". A value of "deprecated" indicates that
implementations should consider migrating away from this object and
that its implementation is no longer required to be considered
conformant. A value of "obsolete" means the object should not be
implemented. Deprecated and obsolete content is never removed from
the document and its element name can never be re-used.
In XML syntax
current
In compact syntax
>> dml:status [ "current" ]
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10.4. Additional Conformance Information
Additional information about conformance should be specified using a
documentation tag.
Examples of additional conformance information that may be useful to
provide includes how implementations can specify specific exceptions
to required conformance, dependencies between elements (in order to
do A, you need to first do B) and conditional conformance (if BGP,
then ...).
10.5. Schema Level Conformance - Server-side
In order to claim compliance to a schema, all elements and attributes
need to conform to their given cardinality definitions and all
elements and attributes with a status of "current" and with a
cardinality greater than or equal to one need to be supported. In
addition, all of the operations listed by the minAccess attribute
need to be supported.
10.6. Schema Level Conformance - Client-side
Client-side conformance is a method of indicating whether presence of
an object is required in order to be a valid configuration. A new
processing annotation is added called mustUse to support this. When
present, this object is required in a valid configuration and when
not present, it is optional in a valid configuration. Note that
optional objects may have default values to enable them to have
values in the configuration without being explicitly set by the
client.
In XML syntax
In compact syntax
>> dml:mustUse []
11. Grading against the requirements
The following outlines how the RCDML requirements [13] (version -03)
are met by this solution or when applicably, why it was felt
requirements should not be met.
11.1. Met requirements
The following requirements are all met by this proposal.
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o 3.1.1 Notification Definition
o 3.1.2 Notification Get
This proposal can be used to define notifications reusing or
separately defining content in any proportion. Two example
notiications are shown in Section 9.3.
o 3.1.3 Locking
This solution does not preclude the fine-grain locking mechanism
proposed in the partial locking draft. That approach primarily is
built using XPath and it is well- understood how to use XPath with
Relax NG-based solutions.
o 3.1.4 All Base Operations
Operations using get, get-config, and edit-config are described in
Section 9.2 and Section 9.1.
o 3.1.5 Define new NETCONF Operations
o 3.1.6 Separation of Operations and Payload
The proposal allows definition of new Netconf actions. An example is
in Section 9.4. The dml:infoType annotation provides a clear
distinction between actions and incorporated data.
o 3.1.7 Error Annotation
Netconf-specific error messages can be defined using 'dml:netconf-
error-app-tag' error annotation attributes added to embedded
Schematron rules as described in Section 9.5.
o 3.1.8 No Mixed Content
The Schematron rules run against each data model (described in
Section 6) prevent introducing mixed content.
o 3.2.1 Human Readable
o 3.2.2 Machine Readable
o 3.2.3 Textual Representation (72 column ASCII)
o 3.2.7 Diff Friendly
These are inherent features of Relax NG Compact.
o 3.2.4 Document Information
The proposal uses DublinCore elements and the dml:organization and
dml:email elements, as described in Section 7.
o 3.2.5 Change control
o 3.2.6 Dependency risk reduction
Relax NG and Schematron (and the rest of DSDL) are ISO standards.
DublinCore is a publication of the [openmetadata alliance?] We can
reference specific versions of these references. The DML annotations
described in this proposal would have IETF change control.
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o 3.2.8.1. Descriptions using Local Languages
o 3.2.8.2. UTF-8 Encoding
o 3.2.8.3. Localization Support
o 3.2.8.4. Error String Localization
The proposal uses UTF-8 encoding and allows arbitrary text
annotations in any language. Localization of a data model is a user-
interface issue. An additional annotation (not defined here) could
be added to provide localized names for elements for automatically
generated web forms for example. Error string localization is shown
in Section 9.5.
o 3.2.8.5. Tag Names and Strings in Local Languages
While XML elements can be named with non-ASCII characters in Relax
NG, this practice is discouraged by the IETF. If desirable, a
warning or error could be incorporated into the data model Schematron
rules described in Section 6 if non-ASCII characters are present in
element and attribute names. Alternatively, DSDL Part 8 - The
Document Schema Renaming Language (DSRL) could be used to transalte
between localized and canonical tag names.
o 3.3.1 Modularity
o 3.3.2 Reusable Definitions
o 3.3.3 Modular extension
Relax NG allows schema to be defined in separate files, and to both
reuse and extend parts of schema (patterns) defined in separate
files. The full example in Section 12 shows how the DHCP module is
extended with the timezone option in dhcp-tz.rnc and the WINS server
option in dhcp-wins.rnc without modifying the original dhcp.rnc
schema or its annotations. A dhcp+extensions.rnc file needed a
single line added to include the new extension. Multiple extensions
to the same portion of the schema are allowed. To add a new module,
a single line is added to the top-level "config-root.rnc" file.
Pattern names do not need to be unique among multiple modules. More
extensibility issues are discussed in Section 8.
o 3.4.1 Default values on the wire
Default values are mentioned in Section 7. Default values are
specific to a specific version of the data model. Data with a
default value can be excluded from an instance document if the
carrying protocol provides some way to discriminate between
configuration with and without default values. When used with
Netconf, the edit config will exclude default values unless defaults
are explicitly requested in a get or get-config request.
o 3.4.2.1 Ordered Lists
o 3.4.2.2 Order within containers
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o 3.4.2.3 Interleaving
Relax NG supports both ordered and unordered collections of non-like
elements through the "," (sequence) and "&" (interleave) operators.
While interleaved collections proxide more flexibility, sequenced
content is supported for backwards compatibility, etc. The dml:list-
order annotation can be used as a semantic hint so that Netconf
agents know if the order of a list is semantically meaningful.
o 3.4.3.1 Validate instance data
o 3.4.3.2 Tools to validate instance data
Instance data is valid if it validates against both Relax NG (with
emebbeded Schematron and the machine-generated Schematron schemas for
uniqueness and referential integrity. Validators for these schema
exist.
o 3.4.4 Instance Canonicalization
To canonicalize an instance of a data model created using this
proposal, follow the rules defined in [3] and then for element or
attribute values which are of type token or list, replace any
sequence of whitespce characters with a single space (0x20) character
and remove any leading or trailing whitespace.
o 3.4.5 Character set encoding
o 3.4.6 Model instance localization
Relax NG handles UTF-8 data correctly. While element and attribute
names are allowed to consist of non-ASCII data, this usage is
strongly discouraged. Wherever character content occurs, the data
model can include multiple versions of this content with xml:lang
attributes to allow for localization.
o 3.5.1 Human readable semantics
o 3.5.2 Basic types
o 3.5.3 Handling opaque data
The Relax NG Compact syntax has a human readable syntax. The manual
and schematron validation rules are also human readable. Relax NG
includes a set of basic data types and allows the use of external
datatype libraries, including the XML Schema data type library. An
appendix also includes a reusable library of content types commonly
used in network management.
o 3.5.4.1 Define Keys
o 3.5.4.2 Deep Keys
The proposal describes a mechanism for defining keys in Section 4.2.
These can be compound and/or arbitrarily deep keys.
o 3.5.5.1 Simple Relationships
The key and keyref annotations (described in Section 4.2 and
Section 4.3) define a formal 1:1 or 1:n relationship between objects
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in different hierarchies. These relationships can be formally
validated.
o 3.5.5.3 Retrieve Relationships instance
The value of the element that the keyref processing annotation was
attached to will provide the relationship instance information in the
NETCONF content.
For example, the keyref definition for the interface element
element interface-filter {
element interface {
xsd:token
>> dml:keyref ["//int:interface"]
}+
}
Has an instance of
lo0
en2
which is the instance of the particular interface involved in this
reference.
o 3.5.6. Hierarchical Data
The proposal supports hierarchical data of arbitrary depth.
o 3.5.7.1. Referential Integrity
The proposal supports validation of complex relationships.
Furthermore, as discussed in Section 5, the proposal supports three
"phases" of validation according to context.
o 3.5.8 Characterize Data
Data is characterized as configuration, status, statistics,
notification, and action using the dml:infoType annotation discussed
in Section 4.5.
o 3.5.9.1. Default Values
Static default values are defined using the Relax NG DTD
compatibility 'defaultValue' annotation.
o 3.5.10.1. Formal Description of Constraints
o 3.5.10.2. Multi-element Constraints
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o 3.5.10.3. Non-Key Uniqueness
This proposal supports contraints using human-readable and/or inline
Schematron as described in Section 4.6. Range and pattern
constraints are part of the XML Schema Datatypes library and reused
by Relax NG. A shortcut for constraining uniqueness is described in
Section 4.1.
o 3.5.11 Units
A unit annotation is defined and described in Section 7.
o 3.5.12 Define actions
This is a duplicate of requirement 3.1.5.
o 3.6.1.1. Language Versioning
o 3.6.1.2. User Extensions
o 3.6.1.3. Mandatory Extensions
The data modeling annotations (DML for convenience) defined in this
proposal are extensible. The version of these annotations is
documented in a dmlVersion attribute of the dml element. Users can
add additional DML element and attribute annotations as needed.
These are ignored if not understood unless they contain a namespace
name which is in the dml:mustUnderstand list of namespace prefixes.
o 3.6.2.1. Model Version Identification
Each data model module needs to have a dml:version annotation on its
top-level (root) element.
o 3.6.2.2. Interaction with defaults
In this proposal, defaults are only valid for a specfic version of a
data model. If the client does not have the current version of the
data model it cannot make any assumptions about default values in
use.
o 3.6.2.3. Conformance Interference
[TODO].
o 3.6.2.4. Obsolete Portions of a Model
The dml:status annotation is used to mark portions of a schema
deprecated or obsolete.
o 3.6.3.1. Schema Version of Instance
Each data model module is encouraged to include a dmlVersion
attribute on its root element with the version of the data model
generated. The schematron validator for data models described in
Section 6 can generate a warning or error if a data model does not
include such an attribute.
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o 3.6.3.2. Interaction with default Values
Use of defaults is discussed extensively in Section 8.4.
o 3.6.3.3. Backwards Compatibility
o 3.6.3.4. Forwards Compatibility
These issues are discussed in detail in Section 8.
o 3.6.3.5. Must-Understand Model Extensions
Clients which do not support a namespace indentified in the namespace
prefix list in a dml:mustUnderstand element or attribute need to
generate an error. This element or attribute can be added either
under the top-level element of a module, the top-level configuration
element, or as an attribute to the appropriate Netconf RPC element.
o 3.7.1. Conformance to the Modeling Language
An implementation conforms to this proposal if:
1. it automatically validates instance documents using a conformant
Relax NG validator;
2. it automatically validates instance documents using any inline
Schematron validation rules for the appropriate phase using a
conformant Schematron validator; and
3. it verifies 'unique', 'key', 'keyref'. 'mustUse' and 'infoType'
constraints on instance documents as described in Section 4.
Any other implementation which validates equivalently is also
conformant.
o 3.7.2.2. Server Conformance to Schema
o 3.7.2.3. Client Conformance To Schema
o 3.7.2.4. Versioned Conformance
These issues are discussed in detail in Section 10.
o 3.8.1. Standard Technology
This proposal maximizes reuse of standard technology in the form of
ISO DSDL Part 2 (Relax NG), ISO DSDL Part 3 (Schematron), the Relax
NG DTD compatibility annotations, and the DublinCore metadata
annotations.
o 3.8.2. Translate Models to Other Forms
The syntax portion of the model definition proposed by this document
already uses Relax NG. This format can be converted to XSD (W3C XML
Schema) automatically using existing tools (e.g. Trang) with a few
simple limitations related to inherent limitations in XSD. For
example, XSD does not support the interleave pattern, so interleaved
element would not be allowed or would need to be converted to choice
blocks which are compatible with XSD substitution groups.
The conversion is very slightly lossy. The start pattern in Relax NG
defines the root XML element. This information is lost in
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translation as there is no applicable concept in XSD. Other than
that, no information is lost.
o 3.8.3. Minimize SMI Translation Pain
SNMP was primarily used for operational data while NETCONF will be
used for both configuration and operational data. We therefore
believe it is more important to define a useful set of datatypes
which are a good fit for NETCONF rather then translating straight
from SMI. The emphasis is on being able to exploit data type
definitions from the XML world, such as W3C XML Schema Datatypes
definitions and the relax NG native datatype library. That having
been said, it is possible to define a data type library with a
comparable set of definitions to provide parity to the ones used in
SMI. A hopefully suitable data type library is defined in
Appendix C.
o 3.8.4. Generate Models from Other Forms
The standard XML representation for UML is the XML Metadata
Interchange (XMI) format. It is possible to generate Relax NG and
the annotations described here using an XSLT transformation
stylesheet from XMI when the UML uses a compatible subset of concepts
(e.g. no many-to-many relationships). Converting between UML and
Relax NG is discussed in the van der Vlist Relax NG book in Chapter
14, Section 3 [34].
o 3.8.5. Isolate Models from Protocol
This proposal has a clear separation of generic data modeling
features and a very rich Netconf binding.
o 3.8.6. Library Support
Relax NG is supported in dozens of commercial and open source XML
editors, validators, and XML libraries. Schematron is implemented in
a handful of commercial and open source products. Use of schematron
for validation is not strictly necessary, since validation rules are
also presented in human-readable text. Any implementation which
validates correctly is acceptable. Since DSDL is an ISO standard and
the W3C is incorporating parts of DSDL in its newer specification, it
is likely that implementation of these specification will increase.
11.2. Met applicable subset
o 3.8.7. RFC 3139 Considerations
The scope of the NETCONF data model work is 'Device-Local
Configuration'. Many of the requirements identified in this RFC are
met by the NETCONF protocol, independent of the features of the data
modeling language choice. The solution does specifically meet the
requirement for data-specific errors identified in requirement 10 as
well as provide for the extensibility of configuration data that
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requirement 14 is looking for.
o 3.8.8. RFC 3216 Considerations
Some of the requirements developed and captured during the
development of SMIng are relevant to this discussion. Others are
applicable to very specific protocol nuances of either SNMP or
COPS-PR or specific use cases for these technologies that are likely
not relevant to NETCONF. The requirements which are the most
relevant to this discussion are reflected in the list above.
11.3. Not Met
o 3.5.5.2. Many-to-Many Relationships
The authors did not see a compelling need for many-to-many
relationships as a native feature of the data modeling solution. In
most cases, this could be emulated as follows. Consider a many-to-
many relationship between ports and interfaces. Each port can
contain a list of keyrefs to interfaces. Likewise, each interface
can contain a list of keyrefs to ports.
o 3.5.7.2. Extended Referential Integrity
In order to evaluate if this solution support referential integrity
checks against pre-configured resources, we need to make some
assumptions on how pre-configuration is modelled. If pre-configured
resources are part of the configuration with special status
information to indicate that the underlying hardware or software is
currently not installed, then the same validation rules used for
present resources applies. For example, the validity of referenced
resources in keyref definitions can be verified. Additional
referential checks could be added that are aware of whether equipment
is pre-configured or present and respond appropriately.
Validating against unreachable resources and validating against
operational data runs into issues that have more to do with network
element limitations then with the choice of specification language.
The current operational state on the network element is related to
the current configuration, which is likely different then the
operational state that will result once the configuration is applied.
While some network elements are able to support determining the new
operational state prior to the configuration being committed, this
feature may be beyond the ability of most NETCONF-managed network
elements to provide. While Schematron can in theory support checks
of this nature, we feel this is an advanced feature and not one we
should be focusing on at present.
o 3.5.9.2 Dynamic Defaults
Dynamic default values are very complex. They introduce brittleness
in the system. The additional bandwidth of sending configuration
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information which has a dynamic default is minor and presents an
opportunity for significant simplification. Therefore this proposal
does not address dynamic defaults. If desirable, they could be added
as a separate extension (possibly introduced with the mustUnderstand
annotation). Any such extension would probably use XPath expressions
to formally describe the dynamic relationships.
o 3.7.2.1. Conditional Conformance
This proposal does not support conditional conformance. Conditional
conformance in the past introduced a considerable amount of
complexity with very little gain and occasionally major
interoperability problems. As such, this proposal does not support
conditional conformance. Conformance is implemented at the
granularty of an XML namespace.
12. Full Examples
The example below
In order to fit within 72 characters in width, the pattern
restriction on 'ip-address-content' had to be split across two lines.
This is indicated by the '~' operator in the example. This operator
in Relax NG Compact is equivalent to concatening the two lines into a
single quoted string literal.
# config-root.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
namespace cfg = "http://example.org/ns/cfg"
start = element-config
element-config = element cfg:config { config-contents }
config-contents = empty
config-contents &= external "interfaces.rnc" ?
config-contents &= external "dhcp.rnc" ?
# interfaces.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace xsd = "http://www/w3/org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace sch = "http://www.ascc.net/xml/schematron"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
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namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
namespace int = "http://example.org/ns/int"
default namespace = "http://example.org/ns/int"
start = element-interfaces
element-interfaces = element interfaces {
element-interface+
>> dc:title [ "Example Interfaces schema fragment" ]
}
element-interface = element interface {
element ifIndex { xsd:token },
element ifType { xsd:token }
>> dml:key [ "ifIndex"]
>> dml:version ["1.0"]
}
# dhcp+extensions.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"
include "dhcp.rnc" # base module
include "dhcp-tz.rnc" # timezone option extension
include "dhcp-wins.rnc" # WINS server option extension
# dhcp.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace xsd = "http://www/w3/org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace sch = "http://www.ascc.net/xml/schematron"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
namespace dhcp = "http://example.org/ns/dhcp"
namespace int = "http://example.org/ns/int"
namespace nt = "http://example.org/ns/net-types"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
default namespace = "http://example.org/ns/dhcp"
include "network-types.rnc"
start = element-dhcp
element-dhcp = element dhcp {
global-timer-elements,
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element-subnet*,
element-shared-network*
>> dc:title [ "Example schema for DHCP server" ]
>> dml:version ["1.0"]
>> dc:type ["Dataset"]
>> dc:creator [ "Rohan Mahy" ]
>> dml:organization [ "as an individual" ]
>> dml:contact [ "mailto:rohan@ekabal.com" ]
>> dc:created [ "2008-02-13" ]
}
global-timer-elements = (
[
sch:pattern [
sch:rule [
context = "//dhcp:dhcp"
sch:assert [
test = "dhcp:default-lease-time <= dhcp:max-lease-time"
"Default lease time cannot be larger than maximum lease time"
]
]
]
]
element default-lease-time {
xsd:unsignedInt
>> compat:defaultValue ["3600"] >> dml:units ["s"]
}?,
element max-lease-time { xsd:unsignedInt
>> dml:units ["s"] }?
)
element-shared-network = element shared-network {
attribute name { token },
element-subnet*
}
element-subnet = element subnet {
element-network,
element-prefix-length,
element-range?,
element-dhcp-options?,
element max-lease-time {
xsd:unsignedInt
>> dml:units ["s"]
>> dml:status ["deprecated"]
}?,
element leases {
element-lease*
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>> dml:infoType ["status"]
}?,
element-interface-filter?
>> dml:key ["concat(network, '/', prefix-length)"]
>> dml:manual-validation-rule [
"Verify that none of the subnets overlap with other subnets." ]
}
element-network = element network {
ipv4-address-content
}
element-prefix-length = element prefix-length {
xsd:short { minInclusive = "0" maxInclusive = "32" }
}
element-range = element range {
element low { ipv4-address-content }?,
element high { ipv4-address-content }?
>> dml:existence []
>> dml:manual-validation-rule [
"Verify the range is within the subnet." ]
}
element-dhcp-options = element dhcp-options {
element-router-list-option? &
element-domain-list-option? &
element-custom-option*
}
element-lease = element lease {
attribute ip-address { ipv4-address-content },
element starts { xsd:dateTime },
element ends { xsd:dateTime },
element mac-address { mac-address-content }
>> dml:key ["@ip-address"]
}
element-router-list-option = element router-list {
element router { ipv4-address-content }+
>> dml:order ["user-order"]
}
element-domain-list-option = element domain-list {
element domain { token }+
}
element-custom-option = element custom {
attribute option { xsd:unsignedByte },
(
element ip-address { ipv4-address-content }
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| element string { string }
)
>> dml:key ["@option"]
}
element-interface-filter = element interface-filter {
element-interface+
}
element-interface = element interface {
token >> dml:keyref ["//int:interface"]
}
# dhcp-tz.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"
namespace tz = "http://example.org/ns/dhcp/timezone"
element-dhcp-option &= element tz:timezone { token }?
# dhcp-wins.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"
namespace wins = "http://example.org/ns/dhcp/wins-option"
element-dhcp-option &= element wins:wins-server { token }*
#network-types.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
namespace xsd = "http://www/w3/org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace sch = "http://www.ascc.net/xml/schematron"
namespace dc = "http://purl.org/dc/terms"
namespace dml = "http://example.org/ns/dml"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
ipv4-address-content = xsd:token { pattern =
"((25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])\.){3}" ~
"(25[0-5]|2[0-4][0-9]|1[0-9][0-9]|[1-9][0-9]|[0-9])"
}
mac-address-content = xsd:token { pattern =
"(([0-9a-fA-F]{2}):?){5}[0-9a-fA-F]{2}" }
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13. "DML" Annotations Schema
Below is the complete Relax NG Compact formal syntax for the
annotations schema.
# dml.rnc
namespace rng = "http://relaxng.org/ns/structure/1.0"
datatypes xsd = "http://www.w3.org/2001/XMLSchema-datatypes"
namespace xml = "http://www.w3.org/XML/1998/namespace"
namespace compat ="http://relaxng.org/ns/compatibility/annotations/1.0"
default namespace = "http://example.org/ns/dml"
start = element-dml
element-dml = element dml {
dmlVersionAttribute? &
dml-contents
}
dmlVersionAttribute = attribute dmlVersion { "1.0" }
dml-contents = (
dataModelVersion &
organization* &
contact-info* &
list-order* &
data-category* &
mustUse-flag* &
container-existence* &
manual-validation* &
units* &
conformStatus* &
mustUnderstand*
)
# Each data model needs a version string
dataModelVersion = element version { xsd:string }
# Information about the data model author(s).
# Seems like this should be in Dublin Core
organization = element organization { string-with-lang }
contact-info = element contact { xsd:anyURI }
# Processing annotations
unique = element unique { xsd:anyURI }
key = element key { xsd:anyURI }
keyref = element keyref { xsd:anyURI }
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data-category = element infoType {
attribute minAccess { list { access-strings }}?,
attribute maxAccess { list { access-strings }}?,
("config" | "status" | "statistics" | "action" | "notify")
>> compat:defaultValue ["config"]
}
access-strings = ( "read" | "write" | "create" | "delete" | "execute" )
mustUse-flag = element mustUse { xsd:boolean
>> compat:defaultValue ["false"]
}
manual-validation = element manual-validation-rule { string-with-lang }
# Semantic hints
list-order = element order {
("any-order" | "user-order")
>> compat:defaultValue ["any-order"]
}
container-existence = element existence { empty }
units = element units {
xsd:string { pattern="[^: \n\r\t]+" }
# allow familiar units, but no whitespace or absolute URIs here
|
xsd:anyURI { pattern="([a-zA-Z][a-zA-Z0-9\-\+\.]*:|\.\./|\./|#).*" }
# allow absolute URIs, plus relative URIs with ./ or ../
# prohibit relative URIs that could look like a unit, ex: m/s
}
# Definition copied from definition of gml:Uomidentifier from
# Section 8.2.3.6 of Geography Markup Language (GML) v3.2.1
string-with-lang = (
attribute xml:lang { xsd:language },
xsd:string
)
conformStatus = element status {
"active" | "deprecated" | "obsolete"
>> compat:defaultValue ["active"]
}
# the mustUnderstand element contains space separated list of namespace
# tokens that need to be supported to correctly process the data model
mustUnderstand = element mustUnderstand { list { xsd:NCName } }
dml-netconf-error-app-tag =
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attribute netconf-error-app-tag { xsd:string }
dml-phase-attribute = attribute phase { "fragment" | "std" | "full" }
dml-moduleDefault = attribute moduleDefault {
xsd:boolean >> compat:defaultValue ["false"]
}
14. Security Considerations
TBD
15. IANA Consideration
This document merely evaluates a possible technical approach. It
requires no action by IANA. A specification that uses this approach
would need to register a namespace with IANA.
16. Contributors
Randy Presuhn contributed to the development of this proposal and
provided useful advice on the extensibility model. Thanks to Alan
Hawrylyshen for an early read.
URIs
[26]
[27]
[28]
[29]
[30]
[31]
[32]
[33]
[34]
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[35]
[36]
[37]
[38]
[39]
[40]
[41]
[42]
[43]
[44]
[45]
Appendix A. XSLT Transform from processing annotation to Schematron
Write up notes on how the XSLT works. Generating rules for
uniqueness and key verification. Walk upward until an element
element (add to front of path) or ref element (recurse) is
encountered. Include namespace prefixes. Continue once more for the
parent element. Generating rules for key verification. Generating
rules for keyref validation. Deleting elements or attributes which
are marked obsolete.
TODO
Appendix B. Schematron for validating data model documents
TODO
Appendix C. Data type library
Part 5 of the DSDL Framework defines a very flexible and powerful
syntax for creating named sets of user-defined datatypes. While this
might be the ultimate way for defining new datatypes, this syntax,
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known as Datatype Library Language (DTLL) [18], is still work in
progress and the number of implementations is quite small.
As an interim solution, the datatypes necessary for NETCONF data
modelling purposes can be provided in two different forms:
1. Generic simple datatypes - various types of numbers, strings,
booleans, dates etc. - are available in all RELAX NG
implementations via the W3C XML Schema Datatypes library [6].
2. Domain-specific datatypes such as IP addresses, DNS domain names
and MAC addresses can be prepared as libraries of patterns
expressed in RELAX NG.
RELAX NG has built-in support for the W3C XML Schema Datatypes
library [6]. In the compact syntax, the namespace of this library
("http://www.w3.org/2001/XMLSchema-datatypes") is declared implicitly
with prefix "xsd". In the XML syntax, the URI of this (or any other)
datatype library must be explicitly declared using the
"datatypeLibrary" attribute.
Usage of datatypes from the XML Schema Library in RELAX NG is
straightforward. For example, an element containing autonomous
system number can be defined as follows:
element asn { xsd:unsignedShort }
Likewise, it is easy to impose additional restrictions by means of so
called facets, for example ranges of permissible values:
element hello-multiplier {
xsd:unsignedByte { minInclusive = "3" maxInclusive = "20" }
}
The most important datatypes provided by the XML Schema Library are
summarized in Table 2.
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+---------------+---------------------------------------------------+
| Type | Meaning |
+---------------+---------------------------------------------------+
| byte | 8-bit integer value |
| short | 16-bit integer value |
| int | 32-bit integer value |
| long | 64-bit integer value |
| unsignedByte | 8-bit unsigned integer value |
| unsignedShort | 16-bit unsigned integer value |
| unsignedInt | 32-bit unsigned integer value |
| unsignedLong | 64-bit unsigned integer value |
| float | 32-bit IEEE floating-point value |
| double | 64-bit IEEE floating-point value |
| string | character string without whitespace normalization |
| token | character string with whitespace normalization |
| boolean | boolean type with values "true" or "false" |
| base64Binary | binary data in base64 encoding |
| anyURI | uniform resource identifier |
| dateTime | date and time value according to ISO 8601 |
+---------------+---------------------------------------------------+
Table 2: Selected datatypes from the W3C XML Schema Type Library
C.1. About Domain-Specific Pattern Libraries
This section contains two library modules with reusable RELAX NG
patterns:
inet-types - common Internet-related datatypes such as IP
addresses and prefixes, port numbers and DNS domain names
ieee-types - common datatypes defined in IEEE 802 standards: MAC
address, bridge identifier and VLAN identifier.
The patterns defined in these modules can be used, unmodified or with
modifications, in RELAX NG schemas. This is accomplished by
including one or more modules in the schema, for example
include "inet-types.rnc"
In the compact syntax, the way the included pattern definitions are
used is almost identical to the previous case of simple datatype
libraries; the only difference is the absence of a namespace prefix.
In the following example, the "ip-address" pattern is defined in the
"inet-types" module:
element source-address { ip-address }
The patterns in the "inet-types" and "ieee-types" modules are
designed for maximum flexibility. They can be extended or modified
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using standard RELAX NG mechanisms. As an example, consider the
definition of "port-number" pattern that does not allow a zero value.
If a data modeller had an application where the zero value is
meaningful, she could reuse the definition in the following way:
port-number |= "0"
This construct is called "combination by choice" in RELAX NG and is
equivalent to the following definition:
port-number = xsd:unsignedShort { minInclusive = "1" } | "0"
Extension of patterns defined in an external module is possible
through "combination by interleave". For example, if we wanted to
add scope identifier to IP prefixes, we could redefine the "ip-
prefix" pattern as follows:
ip-prefix &= element scope { xsd:token }
This is equivalent to the following definition:
ip-prefix = ((attribute version { "ipv4" }?, ipv4-prefix)
| (attribute version { "ipv6" }?, ipv6-prefix))
& element scope { xsd:token }
Finally, the third possibility for modifying predefined patterns is
to replace selected pattern definitions entirely with our own
versions.
C.1.1. Internet Data Types
# inet-types.rnc
default namespace = "urn:ietf:params:xml:ns:relax-ng:inet-types"
C.1.1.1. ip-version
This pattern defines possible values for IP protocol version. See
RFC 791 [35] and RFC 2460 [36].
ip-version = "unknown" | "ipv4" | "ipv6"
C.1.1.2. dscp
This pattern represents Differentiated Services Code Point. See RFC
3289 [37], RFC 2474 [38] and RFC 2780 [39].
dscp = xsd:unsignedByte { maxInclusive = "63" }
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C.1.1.3. flow-label
This pattern represents the flow label - 20-bit value that is used
for discriminating traffic flows. See RFC 2460 [36].
flow-label = xsd:unsignedInt { maxInclusive = "1048576" }
C.1.1.4. port-number
This pattern represents the port number that is used by transport
layer protocols such as TCP or UDP. See RFC 4001 [40].
port-number = xsd:unsignedShort { minInclusive = "1" }
C.1.1.5. ip-address
This pattern represents IP address (either IPv4 or IPv6). The
version may be indicated in the "version" attribute, otherwise it is
determined from the textual format.
ip-address =
(attribute version { "ipv4" }?,
ipv4-address)
| (attribute version { "ipv6" }?,
ipv6-address)
C.1.1.6. ipv4-address
This pattern represents IPv4 address in the usual dotted quad
notation.
The pattern is referenced by:
o ip-address (Appendix C.1.1.5)
o ipv4-prefix (Appendix C.1.1.9)
o host (Appendix C.1.1.12)
ipv4-address =
xsd:token {
pattern =
"((25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])\.){3}" ~
"(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])"
}
C.1.1.7. ipv6-address
This pattern represents IPv6 address in one of the three textual
formats defined in RFC 4291 [41], section 2.2 (full, shortened and
mixed).
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The pattern is referenced by:
o ip-address (Appendix C.1.1.5)
o ipv6-prefix (Appendix C.1.1.10)
o host (Appendix C.1.1.12)
ipv6-address =
xsd:token {
pattern = "([0-9a-fA-F]{0,4}:){0,7}[0-9a-fA-F]{0,4}"
pattern =
"(([0-9a-fA-F]+:){7}[0-9a-fA-F]+)|" ~
"(([0-9a-fA-F]+:)*[0-9a-fA-F]+)?::(([0-9a-fA-F]+:)*[0-9a-fA-F]+)?"
}
|
xsd:token {
pattern =
"([0-9a-fA-F]{0,4}:){0,6}((25[0-5]|2[0-4][0-9]|" ~
"[01]?[0-9]?[0-9]).){3}(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])"
pattern =
"(([0-9a-fA-F]+:){6}|(([0-9a-fA-F]+:)*[0-9a-fA-F]+)?::" ~
"([0-9a-fA-F]+:)*)((25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9]).)" ~
"{3}(25[0-5]|2[0-4][0-9]|[01]?[0-9]?[0-9])"
}
C.1.1.8. ip-prefix
This pattern represents IP prefix (either IPv4 or IPv6). The version
may be indicated in the "version" attribute, otherwise it is
determined from the textual format.
ip-prefix =
(attribute version { "ipv4" }?,
ipv4-prefix)
|
(attribute version { "ipv6" }?,
ipv6-prefix)
C.1.1.9. ipv4-prefix
This pattern represents IPv4 prefix. Prefix length is specified by
the "length" subelement.
The pattern is referenced by:
o ip-prefix (Appendix C.1.1.8)
ipv4-prefix =
element address { ipv4-address }
& element length {
xsd:unsignedByte { maxInclusive = "32" }
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}
C.1.1.10. ipv6-prefix
This pattern represents IPv6 prefix. Prefix length is specified by
the "length" subelement.
The pattern is referenced by:
o ip-prefix (Appendix C.1.1.8)
ipv6-prefix =
element address { ipv6-address }
& element length {
xsd:unsignedByte { maxInclusive = "128" }
}
C.1.1.11. domain-name
This pattern represents DNS domain name, see RFC 1034 [42] and RFC
1123 [43].
The pattern is referenced by:
o host (Appendix C.1.1.12)
domain-name =
xsd:token {
maxLength = "255"
pattern =
"([A-Za-z0-9]([\-A-Za-z0-9]{0,61}[A-Za-z0-9])?.)*" ~
"[A-Za-z0-9]([\-A-Za-z0-9]{0,61}[A-Za-z0-9])?.?"
}
C.1.1.12. host
This pattern represents either an IP address (IPv4 or IPv6) or a host
name. The type of the contents may be indicated by the "content-
type" attribute, otherwise it is determined from textual format.
host =
( attribute content-type { "ipv4" }?,
ipv4-address)
|
( attribute content-type { "ipv6" }?,
ipv6-address)
|
( attribute content-type { "dns" }?,
domain-name)
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C.1.2. IEEE Data Types
# ieee-types.rnc
default namespace = "urn:ietf:params:xml:ns:relax-ng:ieee-types"
C.1.2.1. mac-address
This pattern represents an IEEE 802 MAC address in the canonical
format.
mac-address = xsd:token {
pattern = "([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}"
}
C.1.2.2. bridgeid
This pattern represents an identifier of a MAC bridge. See IEEE
802.1D-2004 [44], Section 9.2.5.
bridgeid = xsd:token {
pattern = "[0-9a-fA-F]{4}:([0-9a-fA-F]{2}:){5}[0-9a-fA-F]{2}"
}
C.1.2.3. vlanid
This pattern represents a 12-bit VLAN identifier that is used as a
VLAN tag in IEEE 802.1Q frames. See IEEE 802.1Q-2005 [45].
vlanid = xsd:unsignedShort {
minInclusive = "1"
maxInclusive = "4094"
}
Appendix D. DHCP schema in Relax XML format
For those who prefer the XML syntax of Relax NG, the "dhcp.rnc" file
was converted to "dhcp.rng" using Trang. Some additional whitespace
was added to improve readability and to make the document fit in 72
characters.