Network Working Group P. Stickler Internet-Draft Nokia Research Center Expires: September 5, 2002 March 7, 2002 The 'voc:' URI Scheme for Vocabulary Terms and Codes draft-pstickler-voc-01 Status of this Memo This document is an Internet-Draft and is in full conformance with all provisions of Section 10 of RFC2026. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." The list of current Internet-Drafts can be accessed at http:// www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 5, 2002. 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". Stickler Expires September 5, 2002 [Page 1] Internet-Draft The voc: URI Scheme March 2002 Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. BNF for the 'voc:' URI Scheme . . . . . . . . . . . . . . . . . 3 3. Hierarchical Characteristics of 'voc:' URIs . . . . . . . . . . 4 4. Support for Autogenerated Vocabularies . . . . . . . . . . . . . 6 5. Security Considerations . . . . . . . . . . . . . . . . . . . . 6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 7 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 8 Stickler Expires September 5, 2002 [Page 2] Internet-Draft The voc: URI Scheme March 2002 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" [6] 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. 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[1], 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 Stickler Expires September 5, 2002 [Page 3] Internet-Draft The voc: URI Scheme March 2002 may be preceded with * 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)" [2]. The definition of UUID is adapted from the Internet Draft draft-kindel-uuid-uri-00 [5] defining the UUID string representation conforming to ISO-11578 [4] and adopted by RFC 2518 "HTTP Extensions for Distributed Authoring -- WEBDAV" [3]. 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: UUID = 8hex "-" 4hex "-" 4hex "-" 4hex "-" 12hex hex = digit | "a" | "b" | "c" | "d" | "e" | "f" host = user = digit = uchar = 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" [6] 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. E.g. the following 'voc:' URI voc://getty.edu/TGN/World/North_and_Central_America/United_States/New_Hampshire/Hillsborough/Manchester Stickler Expires September 5, 2002 [Page 4] Internet-Draft The voc: URI Scheme March 2002 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 URI denoting this URI scheme, though it is not itself a valid URI according to this URI scheme. Stickler Expires September 5, 2002 [Page 5] Internet-Draft The voc: URI Scheme March 2002 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] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES", RFC 822, August 1982. [2] Berners-Lee, T., Masinter, L. and M. McCahill, "Uniform Resource Locators (URL)", RFC 1738, December 1994. [3] Goland, Y., Whitehead, E., Faizi, A., Carter, S. and D. Jensen, "HTTP Extensions for Distributed Authoring -- WEBDAV", RFC 2518, February 1999. [4] International Organization for Standardization, "ISO/IEC 11578:1996 Information technology -- Open Systems Interconnection -- Remote Procedure Call", August 2001. [5] Kindel, C., "The uuid: URI scheme", November 1997, . [6] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. Stickler Expires September 5, 2002 [Page 6] Internet-Draft The voc: URI Scheme March 2002 Author's Address Patrick Stickler Nokia Research Center Visiokatu 1 Tampere 33720 FI EMail: patrick.stickler@nokia.com Stickler Expires September 5, 2002 [Page 7] Internet-Draft The voc: URI Scheme March 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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