Network Working Group P. Stickler Internet-Draft NRC Expires: October 12, 2002 April 13, 2002 The 'val:' URI Scheme for Denoting and Describing Datatype Values draft-pstickler-val-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 October 12, 2002. Copyright Notice Copyright (C) The Internet Society (2002). All Rights Reserved. Abstract This document describes the 'val:' Uniform Resource Identifier (URI) scheme for denoting and describing datatype values which are represented by a pairing of the datatype and a lexical form. Stickler Expires October 12, 2002 [Page 1] Internet-Draft The 'val:' URI Scheme April 2002 Table of Contents 1. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 2. BNF for the 'val:' URI Scheme . . . . . . . . . . . . . . . . . 4 3. Security Considerations . . . . . . . . . . . . . . . . . . . . 4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 5 Full Copyright Statement . . . . . . . . . . . . . . . . . . . . 6 Stickler Expires October 12, 2002 [Page 2] Internet-Draft The 'val:' URI Scheme April 2002 1. Overview XML Schema [5] defines a simple datatype as consisting of a value space (a set of values), a lexical space (a set of lexical forms, or strings), and an N:1 mapping from members of the lexical space to members of the value space. Thus, in the context of a given datatype, a lexical form (member of the lexical space) denotes one and only one value (member of the value space). Thus the pairing of a datatype and a lexical form unambiguously identifies a specific value of that datatype. The 'val:' URI scheme is intended to provide a simple but consistent means by which a lexical form can be paired with a datatype URI allowing one to denote the datatype value represented by that pairing. Examples: val:(http://www.w3.org/2001/XMLSchema%23integer)15 val:(http://www.w3.org/2001/XMLSchema%23lang)fi val:(http://www.w3.org/2001/XMLSchema%23NMTOKENS)foo%20bar%20bas val:(http://dodo.xyz.net/x-token)foo val:(voc://john.doe@widgets.org/xyzcoord)28%20191%2011 val:(uuid:f81d4fae-7dec-11d0-a765-00a0c91e6bf6)392f291a093 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 'val:' URI syntax. 'val:' URIs are particularly useful for applications such as RDF [4] where one may wish to make statements about such value resources. E.g. to assign language specific labels to members of an enumeration: Finnish Suomi Finska There is the additional benefit in RDF whereby if canonical lexical forms are used, every datatype value represented by a 'val:' URI in an RDF graph will share a common graph node, which both provides a considerable amount of graph compression compared to other literal datatyping schemes as well as facilitates queries or inference based on equality of datatype values. Stickler Expires October 12, 2002 [Page 3] Internet-Draft The 'val:' URI Scheme April 2002 2. BNF for the 'val:' URI Scheme This is a BNF-like description of the 'val:' 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 * to designate n or more repetitions of the following element; n defaults to 0. This BNF description adopts sub-definitions defined in RFC 2396 "Uniform Resource Identifiers (URI): Generic Syntax" [1] which are not repeated here. val-URI = "val:" "(" datatypeURI ")" lexicalForm datatypeURI = absoluteURI [ "%23" fragment ] lexicalForm = 1*uric absoluteURI = fragment = uric = Any occurrences of the characters '(', ')', or '%' in either the absoluteURI or fragment segments must be URI escaped. E.g. the datatype URI "foo:abc(xyz)#def%23bar" with value "zzz" would be encoded as "val:(foo:abc%28xyx%29%23def%2523bar)zzz". Note that the URI scheme prefix "val:" is considered to be a valid URI denoting this URI scheme, though it is not itself a valid URI according to this URI scheme. 3. Security Considerations This document raises no known security issues. References [1] Berners-Lee, T., Fielding, R. and L. Masinter, "Uniform Resource Identifiers (URI): Generic Syntax", RFC 2396, August 1998. [2] Crocker, D., "STANDARD FOR THE FORMAT OF ARPA INTERNET TEXT MESSAGES", RFC 822, August 1982. [3] International Organization for Standardization, "ISO/IEC 11578:1996 Information technology -- Open Systems Interconnection -- Remote Procedure Call", August 2001. Stickler Expires October 12, 2002 [Page 4] Internet-Draft The 'val:' URI Scheme April 2002 [4] Lassila, O. and R. Swick, "Resource Description Framework (RDF) Model and Syntax Specification", February 1999, . [5] "XML Schema ...", . Author's Address Patrick Stickler Nokia Research Center Visiokatu 1 Tampere 33720 FI EMail: patrick.stickler@nokia.com Stickler Expires October 12, 2002 [Page 5] Internet-Draft The 'val:' URI Scheme April 2002 Full Copyright Statement Copyright (C) The Internet Society (2002). All Rights Reserved. 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