Network Working Group P. Stickler
Internet-Draft Nokia Research Center
Expires: July 17, 2002 January 16, 2002
The 'voc:' URI Scheme for Vocabulary Terms and Codes
draft-pstickler-voc-00
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Copyright Notice
Copyright (C) The Internet Society (2002). All Rights Reserved.
Abstract
This document describes the 'voc:' Uniform Resource Identifier (URI)
scheme for vocabulary terms and codes.
The 'voc:' URI scheme also belongs to the class of Hierarchical URI
Schemes as defined in RFC 2396 "Uniform Resource Identifiers (URI):
Generic Syntax".
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Table of Contents
1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. BNF for the 'voc:' URI Scheme . . . . . . . . . . . . . . . . . 4
3. Hierarchical Characteristics of 'voc:' URIs . . . . . . . . . . 5
4. Support for Autogenerated Vocabularies . . . . . . . . . . . . . 7
5. Security Considerations . . . . . . . . . . . . . . . . . . . . 7
References . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 8
Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 9
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1. Overview
The 'voc:' URI scheme is intended for defining controlled
vocabularies, ontologies, or taxonomies of terms, codes, names,
symbols, or other representations of abstract concepts for
communication between web applications. This includes, among other
cases, names used to identify XML content model constructs (element
and attribute names), terms employed by semantic web vocabularies and
ontologies (class, property, and other resource identities in RDF
schemata), and controlled code sets for the classification or
qualification of web resources (standardized codes for language,
geographic region, encoding, etc).
The 'voc:' URI scheme belongs to the class of Hierarchical URI
Schemes as defined in RFC 2396 "Uniform Resource Identifiers (URI):
Generic Syntax" [7] and as such provides for parsing into distinct
subcomponents, each constituting a hierarchically distinct level.
The hierarchical characteristics of 'voc:' URIs are discussed later
in this document.
The 'voc:' URI scheme also belongs to the class of URIs known as
Uniform Resource Terms (URT) which are themselves a subclass of
Uniform Resource Primitives (URP), a class of URI which constitutes a
"WYSIWYG" URI, one which is not dereferencible to and does not denote
another web resource, but constitutes a self-contained resource where
the full realization of that resource is expressed in the URI itself.
For a full discussion of the properties of URPs and URTs, please see
[1]. Familiarity with the concepts defined therein will facilitate
the full understanding of this document.
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Examples:
voc://w3.org/xhtml-1.4/title
voc://w3.org/rdf-2.0/resource
voc://w3.org/rdfs-2.0/subPropertyOf
voc://iso.ch/3166/DK
voc://iso.ch/3166/DK/025
voc://iso.ch/639/fr
voc://iso.ch/639/fre
voc://dublincore.org/1.2/date
voc://dublincore.org/1.2/date/created
voc://prismstandard.org/1.3/copyright
voc://getty.edu/TGN/World/Europe/United_Kingdom/England/Manchester
voc://getty.edu/TGN/World/North_and_Central_America/United_States/New_Hampshire/Hillsborough/Manchester
voc://john.doe@abc.com/tasks/billable/consultation
voc://-/f81d4fae-7dec-11d0-a765-00a0c91e6bf6/date
These examples are provided for illustrative purposes only and do not
necessarily constitute actual URIs. See the BNF definition below for
an explicit definition of 'voc:' URI syntax.
2. BNF for the 'voc:' URI Scheme
This is a BNF-like description of the 'voc:' Uniform Resource
Identifier syntax, using the conventions of RFC 822[2], except that
"|" is used to designate alternatives, and brackets [] are used
around optional or repeated elements. Briefly, literals are quoted
with "", optional elements are enclosed in [brackets], and elements
may be preceded with <n>* to designate n or more repetitions of the
following element; n defaults to 0.
This BNF description adopts sub-definitions defined in RFC 1738
"Uniform Resource Locators (URL)" [3]. The definition of UUID is
adopted from the Internet Draft draft-kindel-uuid-uri-00 [6] defining
the UUID string representation conforming to ISO-11578 [5] and
adopted by RFC 2518 "HTTP Extensions for Distributed Authoring --
WEBDAV" [4].
voc-URI = "voc://" authority [ "/" voc-name [ "/" term-path ] ]
voc-URI = "voc://-/" UUID [ "/" term-path ]
authority = [ user "@" ] host
term-path = term *( "/" term )
term = 1*uchar
voc-name = 1*uchar
; Sub-definitions adopted from draft-kindel-uuid-uri-00:
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UUID = 8hex "-" 4hex "-" 4hex "-" 4hex "-" 12hex
; Sub-definitions adopted from RFC 1738:
host = hostname | hostnumber
hostname = *[ domainlabel "." ] toplabel
domainlabel = alphadigit | alphadigit *[ alphadigit | "-" ] alphadigit
toplabel = alpha | alpha *[ alphadigit | "-" ] alphadigit
hostnumber = digits "." digits "." digits "." digits
user = *[ uchar | ";" | "?" | "&" | "=" ]
lowalpha = "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" |
"i" | "j" | "k" | "l" | "m" | "n" | "o" | "p" |
"q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" |
"y" | "z"
hialpha = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" |
"J" | "K" | "L" | "M" | "N" | "O" | "P" | "Q" | "R" |
"S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z"
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" |
"8" | "9"
alpha = lowalpha | hialpha
digits = 1*digit
alphadigit = alpha | digit
safe = "$" | "-" | "_" | "." | "+"
extra = "!" | "*" | "'" | "(" | ")" | ","
hex = digit | "A" | "B" | "C" | "D" | "E" | "F" |
"a" | "b" | "c" | "d" | "e" | "f"
escape = "%" hex hex
unreserved = alpha | digit | safe | extra
uchar = unreserved | escape
3. Hierarchical Characteristics of 'voc:' URIs
The 'voc:' URI scheme belongs to the class of Hierarchical URI
Schemes as defined in RFC 2396 "Uniform Resource Identifiers (URI):
Generic Syntax" [7] and as such provides for parsing into distinct
subcomponents, each constituting a hierarchically distinct level.
Each 'voc:' URI containing one or more levels beyond the URI
authority implies a 'voc:' URI for each level up to and including the
authority level, though implied 'voc:' URIs need not have any
properties associated with them nor be meaningful to any particular
system.
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E.g. the following 'voc:' URI
voc://getty.edu/TGN/World/North_and_Central_America/United_States/New_Hampshire/Hillsborough/Manchester
implies all of the following superordinate 'voc:' URIs
voc://getty.edu/TGN/World/North_and_Central_America/United_States/New_Hampshire/Hillsborough
voc://getty.edu/TGN/World/North_and_Central_America/United_States/New_Hampshire
voc://getty.edu/TGN/World/North_and_Central_America/United_States
voc://getty.edu/TGN/World/North_and_Central_America
voc://getty.edu/TGN/World
voc://getty.edu/TGN
voc://getty.edu
Note that it is not required that a 'voc:' URI encoded vocabulary
have any levels beyond the first level of terms below the vocabulary
name. Thus, the 'voc:' URI scheme is suitable both for "flat"
namespaces as well as for hierarchical vocabularies or taxonomies.
No special meaning or interpretation is ascribed by this
specification to particular 'voc:' URI levels or to the relations
between 'voc:' URI levels other than the following:
o the first level of an 'voc:' URI corresponds to the authority
defining the vocabulary (which may be implicit in a UUID
vocabulary name as indicated by a hyphen '-')
o the second level of a 'voc:' URI corresponds to the vocabulary
name
o each of the levels beyond the second level correspond to a
vocabulary term
o the resource denoted by the 'voc:' URI for a term level is
subordinate in some manner to all resources denoted by each
term level 'voc:' URI implied by its hierarchical structure
A given application may choose to conduct queries based on implied
superordinate 'voc:' URIs to retrieve any properties of any
superordinate resources which may be relevant to the interpretation
of a given 'voc:' URI.
Other, more specialized, URI schemes which are derived from the
'voc:' URI scheme may ascribe more specific interpretations to
particular levels implicit in the URI as well as more specific
relational semantics between different levels.
Note that the URI scheme prefix "voc:" is considered to be a valid
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URI denoting this URI scheme, though it is not itself a valid URI
according to this URI scheme.
4. Support for Autogenerated Vocabularies
The UUID form of a 'voc:' URI is intended for cases where a
temporary, autodefined vocabulary of terms must be used. This is
especially useful for RDF processors when encountering XML
vocabularies not qualified by XML namespaces. In such cases, an RDF
parser can autogenerate a UUID scope for each instance, to serve as a
unique per-instance vocabulary of local names, which ensures that
identical unqualified (local) names from different instances do not
collide in a knowledge base syndicated from multiple sources. This
provides a more robust and safe treatment of unqualified names than
the 'online:' or 'genid:' treatments employed by most RDF systems to
date.
5. Security Considerations
This document raises no known security issues.
References
[1] Stickler, P., "An Extended Class Taxonomy of Uniform Resource
Identifier Schemes", January 2002, <http://www-nrc.nokia.com/sw/
draft-pstickler-uri-taxonomy-00.html>.
[2] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT
MESSAGES", RFC 822, August 1982.
[3] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource
Locators (URL)", RFC 1738, December 1994.
[4] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D. Jensen,
"HTTP Extensions for Distributed Authoring -- WEBDAV", RFC 2518,
February 1999.
[5] International Organization for Standardization, "ISO/IEC
11578:1996 Information technology -- Open Systems
Interconnection -- Remote Procedure Call", August 2001.
[6] Kindel, C., "The uuid: URI scheme", November 1997, <http://
www.globecom.net/ietf/draft/draft-kindel-uuid-uri-00.html>.
[7] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource
Identifiers (URI): Generic Syntax", RFC 2396, August 1998.
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Author's Address
Patrick Stickler
Nokia Research Center
Visiokatu 1
Tampere 33720
FI
EMail: patrick.stickler@nokia.com
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