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Re: Syntax: Literals and defined datatypes

From: Ian Horrocks <horrocks@cs.man.ac.uk>
Date: Mon, 18 Apr 2011 17:16:51 +0100
Cc: public-owl-comments@w3.org
Message-Id: <977E6F2F-0859-4FE3-A553-F3AE2E096855@cs.man.ac.uk>
To: Markus Krötzsch <markus.kroetzsch@comlab.ox.ac.uk>
I added this to the list of errata [1].


[1] http://www.w3.org/2007/OWL/wiki/Errata

On 8 Mar 2011, at 08:51, Markus Krötzsch wrote:

> Re-reading the OWL 2 specification, I stumbled upon some syntactic issues that I want to record here. Relevant statements:
> (1) OWL 2 allows ontologies to define datatypes DT as "synonyms" for dataranges DR such that "in any expression in the ontology containing such an axiom, DT can be replaced with DR without affecting the meaning of the ontology" [1].
> (2) Dataranges can have a number of forms, using features like union, intersection, and facet restrictions on datatypes [2].
> (3) A literal "consists of a lexical form, which is a string, and a datatype" where the "lexical form of each literal occurring in an OWL 2 DL ontology MUST belong to the lexical space of the literal's datatype." [3]
> I suppose that it was indented to not allow defined datatypes in literals, and that the hint "the datatypes supported in OWL 2 are described in more detail in Section 4" [3] might suggest this (Section 4 defines built-in types, not defined ones). But the normative grammar uses the same non-terminal "Datatype" both in literals and in defined types, and I could not find another statement that disallows defined types in literals explicitly.
> Using defined datatypes in literals would not be an option for OWL DL since there does not seem to be any place where the *lexical space* of defined datatypes is specified; so if it is unclear how to check the requirements of (3). In any case, the direct semantics does not cover this possibility, and it would also not be desirable to evaluate datatype definitions for checking an ontology's syntactic/structural validity.
> Some editorial clarification might be useful here (if the intended editorial update after XML 1.1 completion ever happens).
> Cheers,
> Markus
> [1] http://www.w3.org/TR/owl2-syntax/#Datatype_Definitions
> [2] http://www.w3.org/TR/owl2-syntax/#Data_Ranges
> [3] http://www.w3.org/TR/owl2-syntax/#Literals
> [4] http://www.w3.org/TR/owl2-syntax/#Appendix:_Complete_Grammar_.28Normative.29
> -- 
> Dr. Markus Krötzsch
> Oxford  University  Computing  Laboratory
> Room 306, Parks Road, Oxford, OX1 3QD, UK
> +44 (0)1865 283529    http://korrekt.org/
Received on Monday, 18 April 2011 16:17:15 UTC

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