- From: Nick Gibbins <nmg@ecs.soton.ac.uk>
- Date: Wed, 22 May 2002 17:14:15 +0100
- To: www-webont-wg@w3.org
Slightly later than I'd hoped - apologies. - nmg --------------------------------------------------------------------------- Web Ontology Working Group response to RDF Vocabulary Description Language 1.0: RDF Schema DRAFT 2002-05-22 1. Executive Summary This document is a response by the Web Ontology Working Group (WOWG) to the current RDF Schema working draft [5] published by RDF Core. In general, our response to this draft is positive; several of the existing problems in the previous candidate recommendation [2] have been fixed (including the semantics of repeated rdfs:range and rdfs:domain constraints and the restriction on cycles in rdfs:subClassOf and rdfs:subPropertyOf), which brings the semantics of RDFS into line with those of the Ontology Web Language (OWL) currently under development by WOWG. The majority of the issues that we have with this draft are already covered by the the editorial notes which appear within it. We have restated certain of the points made in these notes where we feel that they are particularly important to the development of OWL. Finally, the explanatory text in this draft is quite sparse and needs a considerable amount of fleshing out. Without further examples and cross-references to the relevant sections of other RDF specifications, it is likely to present a barrier to the understanding of RDF Schema by novice RDF users. 2. Comments 2.1 Section numbering While the overall structure of the RDF Schema document is acceptable, it would benefit from having numbered sections in order to make it possible to refer to specific parts of the document (this would have been useful during the preparation of this response!) 2.2 Typographical errors In Appendix B [5b], the value of the rdfs:comment property on rdfs:subClassOf is incorrect, and appears to have been cut and pasted from the comment for rdf:type. It should read "Represents a specialization relationship between classes of resource", or similar. This error also appears in the table entitled RDF Properties [5a]. 2.3 Changes from previous version This document is likely to be read before the Model Theory, especially by novice users. The changes that have been made to the semantics of multiple rdfs:range and rdfs:domain properties from the previous version [2] are significant, and should be made explicit in this document. Similarly, the document should explicitly state that it is now possible to create cycles in the rdfs:subClassOf and rdfs:subPropertyOf properties. 2.4 rdf:value The document notes that rdf:value [5c] is used to identify "the principal value (usually a string) of a property when the property value is a structured resource", but there is no explanation of what is meant by a structured resource. Is this the same as a structured property value, as mentioned in [3a]? The only existing examples of the use of rdf:value use are in Model and Syntax [1a,1b]. The RDF Issue Tracking document notes [7a] that the Model Theory [6] should state that rdf:value has no specific semantics beyond those ascribed to a property, but it is not mentioned in the MT, nor it is mentioned in the revised RDF/XML syntax [4]. This text would benefit from further clarification and from cross-references to the relevant sections of [1],[3] and [6]. 2.5 Datatypes The ability to talk about datatype values is an important requirement for an ontology language that has been identified by WOWG [8a] and that appears in several of its open issues [9a,9b]. The DAML+OIL language, which WOWG has taken as a starting point for its work, takes an approach to the representation of datatypes which ascribes special semantics to the rdf:value property [10a] (a potential conflict with RDF Core's decision regarding rdf:value, as mentioned in 2.4). The RDF Schema draft makes no mention of datatype issues, nor does it contain placeholders for references to the RDF Datatypes document under development by RDF Core. The RDF Schema document should make clear the relationship between datatypes and schemas; we make this comment here in anticipation of the publication of the RDF Datatypes working draft. 2.6 Containers The section on containers in this document is particularly sparse, and needs more concrete examples and cross-references to the relevant sections in the RDF Primer [3] and Model Theory [6], possibly with a recapitulation of the behaviour of the rdf:li pseudo-property. In addition, although the rdfs:member property that has been introduced in this draft appears in the entailments in the Model Theory [6a], the existing class rdfs:ContainerMembershipProperty does not. Strictly speaking, this is an issue with the Model Theory, rather than the RDF Schema draft; we include it here because we believe that this section needs to be cross-referenced to the Model Theory in order to clarify the definitions. 3. References [1] Resource Description Framework (RDF) Model and Syntax Specification, W3C Recommendation, 22 February 1999 http://www.w3.org/TR/REC-rdf-syntax/ [1a] Qualified Property Values http://www.w3.org/TR/REC-rdf-syntax/#value [1b] Non-Binary Relations http://www.w3.org/TR/REC-rdf-syntax/#ex-NonBinary [2] Resource Description Framework (RDF) Schema Specification 1.0, W3C Candidate Recommendation, 27 March 2000 http://www.w3.org/TR/2000/CR-rdf-schema-20000327/ [3] RDF Primer, W3C Working Draft, 26 April 2002 http://www.w3.org/TR/2002/WD-rdf-primer-20020426/ [3a] Structured Property Values http://www.w3.org/TR/2002/WD-rdf-primer-20020426/#structuredproperties [4] RDF/XML Syntax Specification (Revised), W3C Working Draft, 25 March 2002 http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20020325/ [5] RDF Vocabulary Description Language 1.0: RDF Schema, W3C Working Draft, 30 April 2002 http://www.w3.org/TR/2002/WD-rdf-schema-20020430/ [5a] RDF Properties http://www.w3.org/TR/2002/WD-rdf-schema-20020430/#ch_properties [5b] RDF Schema as RDF/XML http://www.w3.org/TR/2002/WD-rdf-schema-20020430/#ch_appendix_rdfs [5c] rdf:value http://www.w3.org/TR/2002/WD-rdf-schema-20020430/#ch_value [6] RDF Model Theory, W3C Working Draft, 29 April 2002 http://www.w3.org/TR/2002/WD-rdf-mt-20020429/ [6a] RDFS-entailment and RDFS closures http://www.w3.org/TR/2002/WD-rdf-mt-20020429/#rdfs_entail [7] RDF Issue Tracking, 2 May 2002 http://www.w3.org/2000/03/rdf-tracking/ [7a] Issue rdfms-replace-value: Suggestion that the rdf:value property be replaced by rdf:toString http://www.w3.org/2000/03/rdf-tracking/#rdfms-replace-value [8] Requirements for a Web Ontology Language, W3C Working Draft, 7 March 2002 http://www.w3.org/TR/2002/WD-webont-req-20020307/ [8a] Datatypes http://www.w3.org/TR/2002/WD-webont-req-20020307/#req-datatypes [9] Web Ontology Issue Status, W3C Working Draft, 20 May 2002 http://www.w3.org/2001/sw/WebOnt/webont-issues.html [9a] Structured Datatypes http://www.w3.org/2001/sw/WebOnt/webont-issues.html#4.3-Structured-Datatypes [9b] Datatypes http://www.w3.org/2001/sw/WebOnt/webont-issues.html#5.8-Datatypes [9c] Closed Sets http://www.w3.org/2001/sw/WebOnt/webont-issues.html#2.5-Closed-Sets [10] DAML+OIL (March 2001) Reference Description, W3C Note, 18 December 2001 http://www.w3.org/TR/daml+oil-reference [10a] Datatype Values http://www.w3.org/TR/daml+oil-reference#Values --------------------------------------------------------------------------- -- Nick Gibbins nmg@ecs.soton.ac.uk IAM (Intelligence, Agents, Multimedia) tel: +44 (0) 23 80592831 Electronics and Computer Science fax: +44 (0) 23 80592865 University of Southampton
Received on Wednesday, 22 May 2002 12:14:21 UTC