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

From: Jeremy Carroll <jeremy@topquadrant.com>
Date: Wed, 11 Nov 2009 08:48:19 +0100
Message-ID: <4AFA6C43.3030805@topquadrant.com>
To: Alan Ruttenberg <alanruttenberg@gmail.com>
CC: Holger Knublauch <holger@knublauch.com>, Ian Emmons <iemmons@bbn.com>, Simon Reinhardt <simon.reinhardt@koeln.de>, semantic-web@w3.org

>> 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.
>>>
>>>       
Alan - the above statement is simply false. You really should have the 
good grace to admit that you have been caught out.

> 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.
>
>   

If you bothered to read the reference to RFC 3986, 5.1.1 you would see 
that section 5.1 explains how all Web retrievable documents that involve 
relative IRIs have a base.


> So I maintain: the "semantic" part of semantic web technologies, knows
> nothing of xml:base.
>
>   
Quite a change in your position. (I agree with this statement).
Since we were talking about  pragmatic issues to do with managing 
ontologies and namespaces, what is semantically relevant in a semantic 
web document is somewhat of a side issue in this conversation.

>> 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.
>
>   

Use of xml:base is always optional, and the developers of the test case 
infrastructure chose to use that option.

> 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.
>
>   
Now that is a disconnect. XQuery concerns the actual syntactic structure 
of an XML document. This has very little to do with the semantics, and 
except with a lot of care and attention, the systematic use of XQuery 
with semantic web documents will get you into trouble.

(I take it that the implementations you use do not make any local copies 
at all of any of the documents you use ... hmmm ... they must be very 
fast. Here's another part of the OWL2 spec that you seem to have failed 
to read:
http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#Imports
[[
For example, in order to access the above mentioned ontology document 
from a local cache,
]]
which is other words for allowing a copy to be stored locally. Alan, 
please read the specs before making further groundless bold assertions.)

>> , 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.
>
>   
It generally is, but yes - reading the xml:base alone on arbitrary web 
content could result in error.



>> (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
>   

That's an interesting para, thanks for the pointer.
I didn't find the text in the OWL2 specs that actually talks about 
dereferencing the imported IRIs ... do you have a pointer please.

> Regards,
> Alan
>   
Jeremy
Received on Wednesday, 11 November 2009 08:21:20 UTC

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