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

On Wed, Nov 11, 2009 at 2:48 AM, Jeremy Carroll <jeremy@topquadrant.com> wrote:
>
>>> Alan Ruttenberg wrote:
>
>> 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.

5.1.1 describes one of four ways that a base URI can be established,
in this case by embedding a declaration of it explicitly in the
content.  When I said "Not all *serializations* have an xml base." I
meant not all documents use the method described in 5.1.1.  I referred
to  the method in 5.1.3 elsewhere in my message.

> Since we were talking about  pragmatic issues to do with managing ontologies
> and namespaces,

There are ontologies to manage. I contest that there are namespaces to manage.

> 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.

The point was to demonstrate that there are, at the level of XML
itself, mechanisms to determine equality of documents that goes beyond
the surface syntactic structure. OWL's (via RDF/XML) use of XML
similarly is at a level that does not depend on some details of the
surface syntactic structure.

> (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.

I am involved with development of OWL ontologies on a daily basis and
have to deal with performance issues of a variety of sorts. A search
of google will find a reasonable amount of detail on such efforts.

I do use local copies. It is a royal pain. Having different tools
inject idiosyncratic behaviors, such as ignoring owl ontology names
makes it even more difficult, such experience being the impetus behind
my first email in this round.

I proposed, within the working group, that we make this easier, but it
was not considered to be something appropriate for the working group
to undertake in full. There is at least *some* mechanism available
now, via the versionIRI, to make this possible in a supported way.
http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#Versioning_of_OWL_2_Ontologies

In addition there is rich support for caching associated with the http
specifications, should your ontologies be the sort that are on the
web.

> 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.)

I'm sorry, I don't believe I made any assertions which would
contradict this. Could you please cite what I said that makes you
think so?

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

Really? That section says nothing about relative URI computations.

> I didn't find the text in the OWL2 specs that actually talks about
> dereferencing the imported IRIs ... do you have a pointer please.

http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#Ontology_Documents

Ontology documents are not represented in the structural specification
of OWL 2, and the specification of OWL 2 makes only the following two
assumptions about their nature:

* Each ontology document can be accessed via an IRI by means of an
appropriate protocol.
* Each ontology document can be converted in some well-defined way
into an ontology (i.e., into an instance of the Ontology UML class
from the structural specification).

http://www.w3.org/TR/2009/REC-owl2-syntax-20091027/#IRIs discusses
other details, including:

* Each IRI must be absolute (i.e., not relative). [speaking of IRIs in
the structure specification]

* If a concrete syntax uses this IRI abbreviation mechanism, it should
provide a suitable mechanism for declaring prefix names. Furthermore,
abbreviated IRIs are not represented in the structural specification
of OWL 2, and OWL 2 implementations must exhibit the same observable
behavior as if all abbreviated IRIs were expanded into full IRIs
during parsing. Concrete syntaxes such as the RDF/XML Syntax [RDF
Syntax] allow IRIs to be abbreviated in relation to the IRI of the
document they are contained in. If used, such mechanisms are
independent from the above described abbreviation mechanism. The
abbreviated IRIs have the syntactic form of qualified names from the
XML Namespaces specification [XML Namespaces]; therefore, it is common
to refer to PI as a namespace and rc as a local name. This
abbreviation mechanism, however, is independent from XML namespaces
and can be understood as a simple macro mechanism that expands prefix
names with the associated IRIs.


-Alan


>
>> Regards,
>> Alan
>>
>
> Jeremy
>
>

Received on Wednesday, 11 November 2009 15:52:43 UTC