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Re: Where are the semantics in the semantic Web?

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Thu, 24 Nov 2005 15:14:51 -1000
Message-ID: <4386658B.7020902@ibiblio.org>
To: public-sws-ig@w3.org

By semantics, we mean a machine-readable and interoperable way of
exchanging data cross systems, semantics as in model theory ala Kripke
not semantics as in real world situations and objects. The trick will be
to get those two to line up and interoperate.

 The only way to make this work is to give it a formal semantics, i.e. a
model-theory that can be used to describe abstractions of real world
("dog" and "airport") , as RDF and OWL have[1] and XML and XML Schema do
not. XML Schemas do *not* provide class definitions of abstractions of
the real world, but provide data-typing and constraint information for a
group of vanilla XML document or data. Those are two *different* things.
Now, they possibly could be bound together as people are looking at
here, but I think saying that data integration and discovery without
agreement can be done in vanilla XML is false without the help of
outside technologies (tagging, SemWeb, etc.).

So - XML and XML Schema are primarily for data exchange when two or more
parties have an agreed upon exchange format, but often in Web Service
discovery and data integration this is not the case [2]. There is a big
difference between data exchange (serializing your data in vanilla
XML/XML Schema) and doing data integration and data discovery. The
question of the hour is - can the SemWeb solve the data
integration/discovery problem, the central issue of the Web?

By its very title, this list-serv is dedicated to that solution. If it
ends up another non-Semantic Web group of technologies accomplishes it,
it will probably be discovered on another listserv :)

 If one really wants to talk about where the philosophy of where the
semantics in the Web are, please do send a paper into our upcoming
workshop[3] on these issues but let's keep this list-serv a bit focused
on the binding issue. And yes - of course - we must keep it simple. But
stuffing complex abstractions of the world into XML documents is
trickier than it looks.

                      -harry halpin
                      University of Edinburgh

Not for XML Schema there was an attempt by Henry Thompson, Phil Wadler,
and more,
but it is proving difficult and nothing is close to standardized, even
if it was, it would
be a formal semantics of data-typing and constraints over vanilla XML.
[2] http://www.w3.org/2004/12/rules-ws/paper/77/

jeff@inf.ed.ac.uk wrote:

>Quoting Jim Hendler <hendler@cs.umd.edu>:
>>So if you said
>>http://ww.cs.umd.edu/hendler/peopleont#firstname then there could be
>>a document at that URI with some text (for people) or RDFS/OWL (for
>>machines) that helped explain your use of the referent.  Even if
>>there isn't, if you and I agreed to use that term in a certain way,
>>we wouldn't have to convince anyone else to agree with us - because
>>someone using a service that took this input would never confuse it
>>as being equal (as it would be in English) to some other
>>http://foo.bar.baz/services/servont#firstname.   In you Xlink-like
>>scheme, there is no way to distinguish different users using the same
>>string, so we need to get the impossible global agreement.  When we
>>use URIs at least that aspect of the problem goes away
>But XML will typically use namespaces.  It's not as if everyone
>who decides to use "firstname" elements much clash with everyone else.
>Of course, it is useful to be able to treat an element name as
>a URL and look up something machine-readable about it.  But
>it's not only RDF/OWL that let you do that; it can also be done
>with XML schemas; and in many cases, schemas can be quite
>straightforwardly read as class definitions.
>There are problems with that approach, and I am no fan of
>XML schemas; but the current approach to the semantic web
>is not perfect either, and I am not convinced there is as
>strong a syntax-vs-semantics difference between them as
>often seems to be suggested.
>In one of your slides, you say "The semantic web exists -- don't
>reinvent it".  But computing and other fields often make progress
>by developing alternatives to existing approaches.  People didn't
>decide "we have a programming language; let's not reinvent that
>by designing a different one".
>I am certainly not saying that the current RDF/OWL/OWL-S approach
>is not worth pursuing, and I like quite a few things about it;
>but I'd also like to see some alternatives pursued as well.
>>  ... if you want to try to get a
>>service language that works by natural language agreement, instead of
>>something more formal, all power to you -- I think it is a doomed
>>enterprise, but I could be wrong
>But a lot of natural language agreement is also needed when
>RDF etc are used.  If I want to know what various Dublin Core
>terms mean, for example, it's some English-language text that
>tells me.  That's how I can tell whether I should use DC "creator"
>or not.
>-- Jeff
Received on Friday, 25 November 2005 01:15:19 GMT

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