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Re: [sdw] Time ontology uses XML Schema Datatypes that are not allowed in OWL 2

From: Elisa Kendall via GitHub <sysbot+gh@w3.org>
Date: Sun, 22 Apr 2018 18:49:23 +0000
To: public-sdwig@w3.org
Message-ID: <issue_comment.created-383403507-1524422962-sysbot+gh@w3.org>
In https://www.w3.org/TR/2012/REC-owl2-syntax-20121211/, section 4 discusses the set of XML Schema Datatypes that are allowable in OWL.  In particular, that section says:

The rest of this section defines a particular datatype map called the OWL 2 datatype map, which lists the datatypes that can be used in OWL 2 ontologies.

You are correct in that this is a bit subtle, and doesn't say specifically that the others cannot be used, but neither the Functional Syntax nor the mapping to RDF semantics says that they are _**available for use**_ without additional very clear semantics being specified and without requiring additional processing support in tools that choose to implement them.  See https://www.w3.org/TR/2012/REC-owl2-rdf-based-semantics-20121211/#Interpretations under Definition 4.1 for a bit more detail.  

Most OWL 2 compliant tools do not allow extensions to the set of core datatypes at all.  If you choose to use them, the tool behavior is not predictable.  The OWL 2 working group had all kinds of discussions about this - you might look at the historical mailing lists for some of the details, and at minutes from working group notes, since I am not sure where the discussion is captured.  I just remember that there were many heated discussions around datatypes and that the ones we excluded were underspecified.  It's just safer not to use them if you want to foster broad adoption by OWL 2 users.  

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