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
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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.
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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
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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.
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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.
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[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
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