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From: Ashok Malhotra <ashok.malhotra@oracle.com>
Date: Mon, 11 Apr 2005 16:11:33 -0700
To: public-swbp-wg@w3.org
CC: w3c-xsl-query@w3.org
Message-ID: <20050411161133372.00000002636@amalhotr-pc>
The W3C XQuery and XSLT WGs asked me to review the document entitled XML Schema Datatypes in RDF and OWL.  The review attached below has been approved by the WGs.  
All the best, Ashok
Review of XML Schema Datatypes in RDF and OWL 
(Editors' Draft 2005/01/27)

The RDF and OWL Recommendations use the simple types from XML Schema and some of the operators from the F&O document. The document we reviewed discusses three questions related to this usage: 

- What URIref should be used to refer to a user defined datatype? 

- Which values of which XML Schema simple types are the same? 

- How to use the problematic xsd:duration in RDF and OWL?

The document does not attempt to answer these questions in a definitive manner but, rather, discusses the pros and cons of different approaches.  

Section 1.3

This section refers to "derivation by list" and "derivation by union".  This is, indeed, the XML Schema 1.0 usage but it has caused widespread misunderstanding as the derived types are not subtypes of the types they were derived from.  This usage is being changed in XML Schema 1.1 to "constructed by list" and "constructed by union".

How to Refer to User-defined Datatypes

Two approaches are discussed:  use the name of the derived typed as a fragment identifier with the Schema target namespace and the SCD approach recommended by XML Schema.

Although it is not our place to make a recommendation here, a couple of points need to be made.  The first approach speaks about the using the URI "of the document".  This usage will cause some members of the Schema WG extreme distress as they take the position that Schemas are not isomorphic to documents.  Thus, "schema target namespace" is recommended.

The use of fragment identifiers is non-standard.  Although others use fragment identifiers in non-standard ways the use needs to be clearly delineated.

The SCDs approach is the approach favored by the XML Schema WG and, although the fragment identifier approach is simpler, please look at the latest SCD draft from XML Schema.  It is possible that they may be willing to enter into a dialog and make changes to the SCD draft to accommodate your needs better. 

3 Comparison of Values

There is an extended disquisition on equivalence of values.  Not much new here.  But please look at the newly introduced promotion scheme from xs:anyURI to xs:string.  Please also note that xs:hexBinary can be cast to xs:base64Binary and that comparisons on values of these two types can be made after casting. 

3.5 eq

The document says that 'eq' returns 'true' or 'false' or that the values are not comparable.  This is not the case.  The 'eq' operator returns a type error if the values are incomparable and returns the empty sequence if one or both operands is the empty sequence.

The final example is incorrect "INF"^^xsd:float eq "INF"^^xsd:float
does return 'true'.

Please use the F&O functions to test for equality.

4. Duration

The document discourages the use of xs:duration and instead recommends the use of xdt:dayTimeDuration and xdt:yearMonthDuration.  We agree.
Received on Monday, 11 April 2005 23:11:52 UTC

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