Re: XML Base (was Re: Ontology modules and namespaces)

On Tue, Nov 10, 2009 at 5:30 PM, Jeremy Carroll <jeremy@topquadrant.com> wrote:
> Hi Alan
>
> you seem to have forgotten yourself, or at least that bit of yourself that
> read the OWL 2 documents.

Don't think so.

>
> Alan Ruttenberg wrote:
>>
>> As far as any of the semantic web technologies go xml:base *does not
>> exist*. The specs know *nothing* about it. Nor should they.
>>
>>
>
> I read:
> http://www.w3.org/TR/2009/REC-owl2-xml-serialization-20091027/#IRIs
> /[[
> MUST/ be resolved against the respective /base IRI/ as specified in the XML
> Base specification [XML Base
> <http://www.w3.org/TR/2009/REC-owl2-xml-serialization-20091027/#ref-xml-base>].
> ]]

This is an aspect of syntax of some serializations of OWL. Not all
serializations have an xml base. Therefore I classify xml:base as
something to do with XML in particular and OWL and RDF only insofar as
OWL can be serialized using XML.

As you point out in your previous email, base and prefixes provide a
way to abbreviate URIs. There is no other specified purpose for them.
In my opinion, any other use for them is a bad idea at least because
xml:base does not exist in all serializations and we want stuff to
work independent of choice of serialization, if at all possible.

So I maintain: the "semantic" part of semantic web technologies, knows
nothing of xml:base.

> I read
> http://www.w3.org/TR/2009/REC-owl2-primer-20091027/#Ontology_Management
> and see the second set of examples using xml:base in both the RDF/XML and
> the OWL/XML

And not in the manchester, nor in the turtle.

> The automated converter for the OWL2 tests appears to add xml:base for both
> RDF/XML and OWL/XML formats,
> e.g. see
> http://owl.semanticweb.org/page/Qualified-cardinality-restricted-int

i.e. it serializes the ontologies properly, by which I mean it
correctly uses the facilities of XML.

> The OWL1 test cases all have explicit xml:base

So? xml:base is not required to be explicit in any XML document. If
not explicit it gets defaulted to the location of the document.

> What is the role of an xml:base, well that is explained in RFC 3986, section
> 5.1.1. This explicitly takes precedence over the retrieval URI, when doing
> base conversions.
>
> In particular, the function of TopBraid Composer which adds an appropriate
> xml:base declaration to a file to allow a copy to be stored locally

zing. The disconnect, as I see it, is the connection between "adds an
appropriate xml:base declaration" and "allow a copy to be stored
locally". There is no such thing in the specification as "allow a copy
to be stored locally". There *is* such a thing as an XQuery giving the
same answer when posed against different XML files.

>, and for relative URI computations to be made correctly seems to be the primary
> intended purpose.

Sure. But making decisions other decisions based on the value of the
xml:base isn't part of the spec, and this is what is being done.
Decisions on what files to import (at least in OWL) are based on the
ontology URI, not the xml:base, except to the extent that in XML
serialized files, the xml:base *might* have been used to parse the
value of the ontology URI.

> (Of course, there is also a normative dependency from OWL2 to xml:base via
> RDF/XML Syntax)

A dependency of certain OWL2 *serializations* on xml:base via both the
RDF/XML syntax and the XML serialization. But OWL the language is
independent of any particular syntax, and so the attempt was to define
the behavior of imports in a way that did not depend on a particular
syntax.  There is a single exception to this goal, there for backwards
compatibility with OWL 1, which has to do with the way that imports of
RDF documents are handled.
http://www.w3.org/TR/2009/REC-owl2-mapping-to-rdf-20091027/#Resolving_Included_RDF_Graphs

Regards,
Alan

Received on Wednesday, 11 November 2009 03:00:35 UTC