Internet DRAFT - draft-flundberg-basestream
draft-flundberg-basestream
Network Working Group F. Lundberg
Internet-Draft Linova
Expires: February 20, 2006 August 19, 2005
BaseStream - A Simple Typed Stream Format
draft-flundberg-basestream-05
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Copyright (C) The Internet Society (2005).
Abstract
BaseStream is a simple binary stream format that serves as a common
base for binary formats like XML provides a base for text formats.
The binary format consists of typed and possibly named data elements.
An instance of the BaseStream format has a corresponding XML
representation that makes it possible to use existing XML tools to
view, edit, validate, and transform BaseStream data.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. BaseStream Definition . . . . . . . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. BaseStream Syntax . . . . . . . . . . . . . . . . . . . . 5
2.3. Future Versions . . . . . . . . . . . . . . . . . . . . . 9
2.4. Application Name . . . . . . . . . . . . . . . . . . . . . 9
3. BaseStream XML . . . . . . . . . . . . . . . . . . . . . . . . 10
4. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 12
5. Security Considerations . . . . . . . . . . . . . . . . . . . 13
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
6.1. Normative References . . . . . . . . . . . . . . . . . . . 14
6.2. Informative References . . . . . . . . . . . . . . . . . . 14
Appendix A. XML Schema for BXML types . . . . . . . . . . . . . . 15
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 21
Intellectual Property and Copyright Statements . . . . . . . . . . 22
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1. Introduction
Binary data is difficult to handle by humans. Therefore text-based
file formats and network protocols are popular. The software for
such stream formats are easier to debug since they use a relatively
human-friendly representation of the data. However, text-based
formats have the following drawbacks compared to binary formats.
o Text-based formats need more bytes to store numerical data than
binary formats do.
o Parsing numerical data represented as text is not efficient
compared to parsing of binary data since since the text
representation is not stored in a way similar to how it is stored
in computer memory.
o It is seldom possible to read only part of a text-based file since
the exact byte offset to a data item is usually not known.
BaseStream is a simple, light-weight, binary stream format consisting
of a sequence of typed and possibly named data elements. The format
is a data serialization format suitable as the base for file formats,
TCP protocols, or any other format that handles sequences of bytes.
Together with appropriate tools a BaseStream can easily be viewed and
edited. BaseStream data is therefore human-friendly, but without the
drawbacks of text-based formats. BaseStream serves as a common base
for binary formats like XML [1] provides a base for text-based
formats.
This document specifies an XML application called BXML or BaseStream
XML. Every BaseStream has a corresponding BXML document. By using
software to convert data between binary BaseStream and BXML, any text
or XML editor can be used to view and edit BaseStream data.
Furthermore, BXML opens up BaseStream data to other XML technologies
such as: data validation with XML Schemas and data transformation
with XSLT (XML Stylesheet Language Transformation).
This document specifies two things.
1. The rules for determining whether a stream is a valid BaseStream
or not, and if it is, how to interpret the bytes of the stream as
numbers and strings.
2. How a BaseStream is represented in XML.
The goal of BaseStream is to make it easy to share binary data and
develop applications that use binary formats.
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2. BaseStream Definition
2.1. Terminology
This subsection defines the specific meaning of some words in this
document.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [8].
A "byte" is an 8-bit data entity.
A "stream" is a sequence of bytes.
A stream is created by a "writer". A writer is an entity capable of
producing a sequence of bytes and a "BaseStreamWriter" is a writer
that produces a BaseStream.
A "reader" reads a stream created by a writer. A "BaseStreamReader"
is a reader that can read a BaseStream and interpret the bytes as
BaseStream elements.
A "format" or "stream format" is a set of rules for a stream that
determines whether or not the stream adheres to the format and how to
interpret the stream bytes as higher level data entities.
"BaseStream" is used to refer either to the stream format defined in
this document or a stream that adheres to the BaseStream format. The
terms "BaseStream format" and "BaseStream instance" can be used to
discriminate the two cases. "BaseStream1" is version 1 of the
BaseStream format, that is, the version described in this document.
The version number is normally left out in this document since the
only version described in this document is version 1.
A "BaseStream application" is a specific format based on BaseStream.
A BaseStream application may put any further restrictions on the
stream as long as every instance of the application is a BaseStream
instance.
Big-endian byte order specifies that multi-byte integers and floating
point numbers are written to a stream with the most significant byte
first.
The following abbreviations are used for basic numerical data types.
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o "INT1", a 8-bit signed integer.
o "INT2", a 16-bit signed integer.
o "INT4", a 32-bit signed integer.
o "INT8", a 64-bit signed integer.
o "FLOAT4", a 4-byte floating point number.
o "FLOAT8", an 8-byte floating point number.
The integer types are 8-bit, 16-bit, 32-bit and 64-bit signed two's
complement integers.
"FLOAT4" and "FLOAT8" are 4- and 8-byte data entities used to store
floating point numbers. These follow the single-precision 32-bit and
double-precision 64-bit formats in the IEEE754 standard [2].
For all the numerical types big-endian byte order is used.
In this document a byte value may be specified with the corresponding
Unicode [5] character in the interval from 0 to 127. For example:
'a' is the value 97. These Unicode character values coincide with
the ASCII [9] character values.
2.2. BaseStream Syntax
A BaseStream consists of a sequence of data elements: Element0,
Element1, Element2, and so on. The elements can be of a simple type,
an array type or the string type. The type is specified by a type
byte. The possible values of the type byte are the Unicode values
for the characters: b, s, i, l, f, d, B, S, I, L, F, D, and U.
There are six simple element types. The simple integer types are the
b, s, i and l-element types. The letters are abbreviations for
"byte", "short", "int", and "long" which are type names in widely
used programming languages. These elements store INT1, INT2, INT4,
and INT8 values respectively. The two simple types for floating
point numbers are the f-element and the d-element which store FLOAT4
and FLOAT8 values. f and d are abbreviations for "float" and
"double".
The array types are the B, S, I, L, F, and D-element types. These
may also be referred to as the B array element type, S array element
type, and so on. These types are used to store an array of INT1s,
INT2s, INT4s, INT8s, FLOAT4s or FLOAT8s respectively. Arrays with
zero elements are allowed.
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The U element type is the string type. Strings are stored using the
Unicode [5] character set that handles all widely used characters.
UTF-8 encoding is used to store the characters as bytes. See RFC
2279 [4] for information on the UTF-8 charset encoding.
Each element may optionally be named. The element name uses a subset
of the ASCII [9] charset. The main reason for this restriction on
the element names is that the name should be possible to type and
print on as many systems as possible. The names are part of the
format/protocol. They are not part of the stream data.
Element0 in a BaseStream has a special meaning. A BaseStream starts
with a byte of value 105 corresponding to 'i' in the ASCII character
set [9]. This is the type byte of Element0. Then there are four
bytes which forms an INT4 with the value 256001. Thus a BaseStream
of version 1 always starts with the following five bytes: 105, 0, 3,
232, 1 which constitute Element0. The purpose of Element0 is to
identify a stream as a BaseStream of a specific version.
After Element0 there are zero to infinitely many user data elements.
The last element is followed by a single byte ('e') used to indicate
the end of the BaseStream. The end byte is important to indicate the
end of a BaseStream when it is a part of another stream.
The array types (B, S, I, L, F, D) and the string type (U) have a
size. The size is the number of integers or floating point numbers
in the array for the array types. For the string type the size is
the number of bytes needed to encode the string in UTF-8. The size
is stored in two ways. See the grammar rules "shortSize" and
"longSize" below. If the size is between 0 and 127 it is stored as
an INT1. If the size is larger than or equal to 128 it is stored as
an INT8.
Below is the syntax specification of the BaseStream format, version
1. Augmented Backus-Naur Form (ABNF) as defined in RFC2234 [3] is
used.
BaseStream1 = Element0 *element e
Element0 = i %d0 %d3 %d232 %d1
; byte 'i' followed by an INT4 with value 256001
element = [elementName] (simple / array / string)
simple =
b INT1 / ; b-element
s INT2 / ; s-element
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i INT4 / ; i-element
l INT8 / ; l-element
f FLOAT4 / ; f-element
d FLOAT8 ; d-element
array =
B size *INT1 / ; B-element
S size *INT2 / ; S-element
I size *INT4 / ; I-element
L size *INT8 / ; L-element
F size *FLOAT4 / ; F-element
D size *FLOAT8 ; D-element
string =
U size utf8
utf8 = <an UTF-8 encoded string>
size = shortSize / longSize
shortSize = <an INT1 between 0 and 127 inclusive>
longSize = minus8 longSizeNumber
minus8 = <an INT1 with the value -8>
longSizeNumber = <an INT8 larger than or equal to 128>
elementName = N nameSize nameString
nameSize = <an INT1 between 1 and 127 inclusive>
nameString = ALPHA 0*126digitLetterOrUnderscore
digitLetterOrUnderscore = ALPHA / DIGIT / UNDERSCORE
ALPHA = %x41-5A / %x61-7A ; A-Z / a-z
UNDERSCORE = %x5F ; '_'
DIGIT = "0" / "1" / "2" / "3" / "4" / "5" / "6" / "7" / "8" / "9"
e = %x65
N = %x4E
b = %x62
s = %x73
i = %x69
l = %x6C
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f = %x66
d = %x64
B = %x42
S = %x53
I = %x49
L = %x4C
F = %x46
D = %x44
U = %x55
INT1 = <previously defined>
INT2 = <previously defined>
INT4 = <previously defined>
INT8 = <previously defined>
FLOAT4 = <previously defined>
FLOAT8 = <previously defined>
We can now list the rules that define the BaseStream format. A
stream is a BaseStream of version 1 if and only if all the following
rules are fulfilled.
1. The stream MUST follow the "BaseStream1" grammar rule.
2. The nameSize integer MUST equal the number of bytes (characters)
in the following nameString.
3. The size integer (grammar rule "size") MUST equal the number of
integers or floating point numbers that follow for the B, S, I,
L, F, and D elements. For the U-element the size MUST equal the
number of bytes needed to encode the UTF-8 string.
4. If a U-element is named "bs_tag" the string value of the element
MUST follow the "nameString" grammar rule. Such an element is
called a tag-element.
5. If a U-element is named "bs_end" the string value MUST be the
empty string (a string with zero characters). Such an element is
called an end-element.
6. At any point in the stream the number of end-elements written to
the stream MUST NOT exceed the number of tag-elements.
7. The total number of end-elements in a BaseStream MUST equal the
number of tag-elements.
8. If Element1 is a U-element named "bs_app" the string value of the
element MUST be the name of the BaseStream application.
The tag-element and the end-element affects how the BaseStream is
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represented as XML. This is treated later in this document.
2.3. Future Versions
Future versions of the BaseStream format are not currently
anticipated, but still prepared for. BaseStreamX is used to denote
version X of BaseStream where X is 1, 2, 3, and so on. Version X of
the format MUST start with with the byte 'i' and then an INT4 with
the value 256000 + X. Any version of BaseStream will thus always
start with the four bytes: 105, 0, 3, 232. The fifth byte is the
BaseStream version. A version number higher than 127 will never be
used.
2.4. Application Name
BaseStream provides a standard way of storing the name of the
BaseStream application in the beginning of the stream. If Element1
of a BaseStream is a U-element named "bs_app" the value of this
element is the name of the BaseStream application. If a BaseStream
application contains the name of the application in the stream it is
RECOMMENDED that it is stored in Element1 as described above. It is
RECOMMENDED that the charset for the application name is limited to
ASCII [9].
To provide unique application names, information about the
application origin, and possibly a reference to a DTD or XML Schema,
a URL may be used as the application name. For example the company X
could call their first version of a 2D plot file format
"http://www.x.com/plot2d/1.xsd". This URL should point to an XML
Schema that can be used to validate the BXML representation of the
BaseStream.
If the application name starts with "http:" and ends with ".xsd" is
is RECOMMENDED that it is considered a URL to a XML Schema file that
can be used to validate the BXML representation of the BaseStream.
The Schema file at the URL location should never change.
If the application name starts with "http:" and ends with ".dtd" is
is RECOMMENDED that it is considered a URL to a Document Type
Definition (DTD) file that can be used to validate the BXML
representation of the BaseStream. The format of a DTD is defined in
the XML standard [1]. The DTD file at the URL location should never
change.
Note that if a URL is used it does not have to point to anything
unless it starts with "http:" and ends with ".xsd" or ".dtd". It can
be used just to provide a unique name for the BaseStream application.
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3. BaseStream XML
This section specifies an XML representation of a BaseStream called
BaseStream XML or BXML. The XML Schema standard ([6] and [7]) is
used to define the exact syntax of the BXML elements.
Any BaseStream instance can be converted to BXML and any BXML
document can be converted to binary BaseStream format. A BaseStream
instance converted to BXML and then back to a binary BaseStream
instance is identical to the original BaseStream instance.
Below is an example of a BXML document that stores plot data.
<?xml version="1.0" encoding="utf-8"?>
<BaseStream>
<i>256001</i>
<bs_app type="U">http://www.x.com/plot2d/1.xsd</bs_app>
<head>
<title type="U">Position vs time</title>
<xLabel type="U">time (s)</xLabel>
<yLabel type="U">pos (m)</yLabel>
</head>
<xData type="F">1.0 2.0 3.0 4.0</xData>
<yData type="F">0.4 1.5 2.0 1.8</yData>
</BaseStream>
A BXML document always has a root XML element called "BaseStream".
The first child of the root element is "<i>256001</i>" which
corresponds to Element0 in the BaseStream. After this the BaseStream
elements are converted to XML by the following rules. The letter X
is used to denote the type character of the element.
1. Any unnamed element is stored as an XML element with the same
name as the type character.
<X>content</X>
The syntax of the X-element content is defined by the XML Schema
type called "X-type". See Appendix A. No XML attributes are
allowed.
2. A named element which is not a tag- or end-element is stored as
an XML element with a name identical to the element name. The
attribute "type" is required and the value of the attribute must
be the type character of the element.
<elementName type="X">content</elementName>
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No other attributes then the type attribute are allowed. The
exact syntax of the X-element content is defined by the XML
Schema rule called "named-X-type". See Appendix A.
3. If the element is a tag-element an unclosed start XML tag is
added to the XML document. The name of the XML element is the
string value of the tag-element. No XML attributes are allowed.
4. If the element is an end-element the last unclosed XML start tag
(created because of a tag-element) is closed by a corresponding
end tag.
For simple types the corresponding XML character contents are
represented as a decimal number. BaseStream to BXML converters are
encouraged to use the canonical lexical representation of these
values as defined in the Schema standard [7].
Array types are written as a sequence of whitespace separated
representations of the corresponding simple type. There is one
exception, the B-element is written as a whitespace separated
sequence of pairs of characters that represent a hexadecimal number
between 0 and 255. The bytes in the B-element are considered
unsigned in this context.
The figure below shows an XML Schema that defines the "plot2d"
BaseStream application for the example given above. The BaseStream
Schema types are left out for clarity. They are defined in Appendix
A.
<xsd:complexType name="plotType">
<xsd:sequence>
<xsd:element name="i" type="versionInt"/>
<xsd:element name="bs_app" type="named-U-type"/>
<xsd:element name="head" type="headType"/>
<xsd:element name="xValues" type="named-F-type"/>
<xsd:element name="yValues" type="named-F-type"/>
</xsd:sequence>
</xsd:complexType>
<xsd:complexType name="headType">
<xsd:sequence>
<xsd:element name="title" type="named-U-type"/>
<xsd:element name="xLabel" type="named-U-type"/>
<xsd:element name="yLabel" type="named-U-type"/>
</xsd:sequence>
</xsd:complexType>
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4. Acknowledgements
The author gratefully acknowledges the contributions of: Lars
Karlsson, Peter Gardfjall and Bjorn Andersson.
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5. Security Considerations
The BaseStream format itself raises no security considerations, but a
badly implemented BaseStreamReader may.
A BaseStreamReader should be able to handle array and string sizes up
to 2^63 gracefully. A simple implementation of a BaseStreamReader
may always allocate new memory for the next element directly after
the type and size information is read. This can result in an out of
memory error that possibly crashes the reader process if the size of
an element is too large. In a network setting an attacker could of
course write any value for the size without necessarily transmitting
the data that should follow.
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6. References
6.1. Normative References
[1] World Wide Web Consortium, "Extensible Markup Language (XML) 1.0
(Third Edition)", W3C XML, February 2004,
<http://www.w3.org/TR/2004/REC-xml-20040204/>.
[2] IEEE, "Standard for Binary Floating-Point Arithmetic, Standard
No.: 754-1985", 1985.
[3] Crocker, D., "Augmented BNF for Syntax Specifications: ABNF",
RFC 2234, November 1997.
[4] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
RFC 2279, January 1998.
[5] The Unicode Consortium, "The Unicode Standard, Version 4.0.0,
defined by: The Unicode Standard, Version 4.0 (Reading, MA,
Addison-Wesley, 2003. ISBN 0-321-18578-1)", 2003,
<http://www.unicode.org/>.
[6] World Wide Web Consortium, "XML Schema Part 1: Structures, W3C
Recommendation 2 May 2001", May 2001,
<http://www.w3.org/TR/2001/REC-xmlschema-1-20010502/>.
[7] World Wide Web Consortium, "XML Schema Part 2: Datatypes, W3C
Recommendation 02 May 2001", May 2001,
<http://www.w3.org/TR/2001/REC-xmlschema-2-20010502/>.
[8] Bradner, "Key words for use in RFCs to Indicate Requirement
Levels", RFC 2119, BCP 14, March 1997.
6.2. Informative References
[9] ANSI, "Coded Character Set--7-Bit American Standard Code for
Information Interchange, ANSI X3.4-1986.", 1986.
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Appendix A. XML Schema for BXML types
<?xml version="1.0"?>
<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema">
<!--
bxml_schema_types.xml
XML Schema types for BaseStream XML representation (BXML)
Frans Lundberg, www.linova.com, 25 April 2003
-->
<!-- VERSION INTEGER -->
<xsd:simpleType name="versionInt">
<xsd:restriction base="xsd:int">
<xsd:minInclusive value="256001"/>
<xsd:maxInclusive value="256001"/>
</xsd:restriction>
</xsd:simpleType>
<!-- SIMPLE TYPES -->
<xsd:simpleType name="b-type">
<xsd:restriction base="xsd:byte"/>
</xsd:simpleType>
<xsd:complexType name="named-b-type">
<xsd:simpleContent>
<xsd:extension base="b-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="b"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="s-type">
<xsd:restriction base="xsd:short"/>
</xsd:simpleType>
<xsd:complexType name="named-s-type">
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<xsd:simpleContent>
<xsd:extension base="s-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="s"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="i-type">
<xsd:restriction base="xsd:int"/>
</xsd:simpleType>
<xsd:complexType name="named-i-type">
<xsd:simpleContent>
<xsd:extension base="i-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="i"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="l-type">
<xsd:restriction base="xsd:long"/>
</xsd:simpleType>
<xsd:complexType name="named-l-type">
<xsd:simpleContent>
<xsd:extension base="l-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="l"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
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</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="f-type">
<xsd:restriction base="xsd:float"/>
</xsd:simpleType>
<xsd:complexType name="named-f-type">
<xsd:simpleContent>
<xsd:extension base="f-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="f"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="d-type">
<xsd:restriction base="xsd:double"/>
</xsd:simpleType>
<xsd:complexType name="named-d-type">
<xsd:simpleContent>
<xsd:extension base="d-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="d"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<!-- ARRAY TYPES -->
<xsd:simpleType name="byteLiteral">
<xsd:restriction base="xsd:string">
<xsd:pattern value="([0-9]|[A-F]){2}"/>
</xsd:restriction>
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</xsd:simpleType>
<xsd:simpleType name="B-type">
<xsd:list itemType="byteLiteral"/>
</xsd:simpleType>
<xsd:complexType name="named-B-type">
<xsd:simpleContent>
<xsd:extension base="B-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="B"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="S-type">
<xsd:list itemType="xsd:short"/>
</xsd:simpleType>
<xsd:complexType name="named-S-type">
<xsd:simpleContent>
<xsd:extension base="S-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="S"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="I-type">
<xsd:list itemType="xsd:int"/>
</xsd:simpleType>
<xsd:complexType name="named-I-type">
<xsd:simpleContent>
<xsd:extension base="I-type">
<xsd:attribute name="type">
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<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="I"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="L-type">
<xsd:list itemType="xsd:long"/>
</xsd:simpleType>
<xsd:complexType name="named-L-type">
<xsd:simpleContent>
<xsd:extension base="L-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="L"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="F-type">
<xsd:list itemType="xsd:float"/>
</xsd:simpleType>
<xsd:complexType name="named-F-type">
<xsd:simpleContent>
<xsd:extension base="F-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="F"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
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<xsd:simpleType name="D-type">
<xsd:list itemType="xsd:double"/>
</xsd:simpleType>
<xsd:complexType name="named-D-type">
<xsd:simpleContent>
<xsd:extension base="D-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="D"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
<xsd:simpleType name="U-type">
<xsd:restriction base="xsd:string"/>
</xsd:simpleType>
<xsd:complexType name="named-U-type">
<xsd:simpleContent>
<xsd:extension base="U-type">
<xsd:attribute name="type">
<xsd:simpleType>
<xsd:restriction base="xsd:string">
<xsd:pattern value="U"/>
</xsd:restriction>
</xsd:simpleType>
</xsd:attribute>
</xsd:extension>
</xsd:simpleContent>
</xsd:complexType>
</xsd:schema>
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Author's Address
Frans Lundberg
Linova
Phone: +46 70 7601861
Email: frans at linova.com
URI: http://www.linova.com
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Intellectual Property Statement
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pertain to the implementation or use of the technology described in
this document or the extent to which any license under such rights
might or might not be available; nor does it represent that it has
made any independent effort to identify any such rights. Information
on the procedures with respect to rights in RFC documents can be
found in BCP 78 and BCP 79.
Copies of IPR disclosures made to the IETF Secretariat and any
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attempt made to obtain a general license or permission for the use of
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specification can be obtained from the IETF on-line IPR repository at
http://www.ietf.org/ipr.
The IETF invites any interested party to bring to its attention any
copyrights, patents or patent applications, or other proprietary
rights that may cover technology that may be required to implement
this standard. Please address the information to the IETF at
ietf-ipr@ietf.org.
Disclaimer of Validity
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
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Copyright Statement
Copyright (C) The Internet Society (2005). This document is subject
to the rights, licenses and restrictions contained in BCP 78, and
except as set forth therein, the authors retain all their rights.
Acknowledgment
Funding for the RFC Editor function is currently provided by the
Internet Society.
Lundberg Expires February 20, 2006 [Page 22]
