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Re: Where are the semantics in the semantic Web?

From: Harry Halpin <hhalpin@ibiblio.org>
Date: Fri, 25 Nov 2005 08:36:09 -1000
Message-ID: <43875999.6080902@ibiblio.org>
To: jeff@inf.ed.ac.uk
Cc: public-sws-ig@w3.org

As for Shi Xuan's case: it seems like if there is enough agreement in
the GIS communtiy, then yes, you could get away with just sticking to
mappings to schemas or *choose your favorite model here*, and if
everyone doing discovery is aware of these schemas or models, then
that's great. But what if they aren't...(and worse, maybe they're a machine)

So, the question is for RDF, and TimBL's bet: is that this RDF thing
provides a useful minimal foundation for all sorts of models, including
logic. It seems to have sort of worked with DL, but basing  FOL on RDF
seems - a bit weird.  And I think the big unspoken thing here is that
almost everyone models things in FOL, and so the Rules Working Group is 
going to have a big impact  on whatever SemWeb Services appear.

Another: are data-types ontologies? Interesting question. Sort of I
would guess, but they come from two entirely different communities. Gut
feeling is that data-types are ontologies for computers that model
things computers care about, not humans.

As for the "semantic chaos" question - I think using tag ontologies
might be one way out.
Seems to be working for deli.cio.us. See www.webpropernames.org for my
take on it.

As for the nice paper produced by Duerst and the various comments of
Jeff, XML ala XLink provides great mapping facilites that have barely
ever been used. However, if RDF/OWL/SoonToBeComingFOLforSemWeb is
abandoned, then basically we're just letting
people link from one XML document to another for Web Services. Now,
maybe people will go through the trouble of defining semantics for the
XML Schemas or GIS models or whatever they link to - and in that case,
let a thousand models bloom.

Or we can all just link to anything, and enter the "no semantics swamp"
:) Read history of AI  such as William Woods  "What's in a Link?
Foundations of Semantic Networks" and the SIGGART questionairre by
Brachman and Smith on "How a KR system is like a Piano"  or ask Winograd
about KRL to see how well this scales :) It generally turns out bad even
when relatively small systems scale.  Those are not available online but
I think writing up a historical look on these issues would be good.

I thought the bet was with Semantic Web Services is that a standard
model would allow us to find and describe WebServices uniformly. Is
RDF/OWL the only game in town? It's the only W3C game..yet. Am I mistaken?

Or we could just all switch to KIF. Would make my life easier for my
particular problem domain at the moment :)

                -harry

Bijan Parsia wrote:

> As much as I hate to participate...
>
> On Nov 25, 2005, at 12:53 PM, jeff@inf.ed.ac.uk wrote:
>
>> Quoting Harry Halpin <hhalpin@ibiblio.org>:
>
> [snip]
>
>>> And, as it must be pointed out again and again, XML does not provide a
>>> formal semantics. It's a serialization format like ASCII - you don't
>>> "reason" or "prove" things with just ASCII, do you?  Think of XML as a
>>> representation format for data, and think of the SemWeb as a
>>> representation format with a formal semantics for *what the data 
>>> refers
>>> to* .
>>
>>
>> I am familiar with that point and don't find it convincing.
>> XML is not just like ASCII, for one thing; ASCII is at a lower
>> level.  While it's true that XML lacks a formal semantics,
>
> [snip]
>
> But it isn't true:
>     http://www.w3.org/TR/2005/CR-xquery-semantics-20051103/
> #sec_preliminaries
>
> """Rigor is achieved by the use of formal notations to represent 
> [XPath/XQuery] objects such as expressions, XML values, and XML
> Schema  types, and by the systematic definition of the relationships
> between  those objects to reflect the meaning of the language. In
> particular,  the dynamic semantics relates [XPath/XQuery] expressions
> to the XML  value to which they evaluate, and the static semantics
> relates  [XPath/XQuery] expressions to the XML Schema type that is
> inferred for  that expression.
>
> The Formal Semantics uses several kinds of formal notations to define 
> the relationships between [XPath/XQuery] expressions, XML values, and 
> XML Schema types.""""
>
> Cheers,
> Bijan.
>

jeff@inf.ed.ac.uk wrote:

>Quoting Harry Halpin <hhalpin@ibiblio.org>:
>
>  
>
>>To use XML Schema to define abstract concepts would force everyone
>>sharing that concept, if it was defined *solely* in terms of XML Schema,
>>to use the same set of XML serializations.
>>    
>>
>
>RDF is not that different.  While it's true that RDF/XML allows
>certain variations, and that there are other syntaxes, in practice
>you are still pretty narrowly constrained; and the downside is
>that the variations allowed in RDF/XML make it difficult to
>process it with many XML tools.
>
>In the end, the different concrete representations of some RDF
>turn into much the same triples.
>
>  
>
>>What is much more interesting and much more feasible for data
>>integration and discovery (and the SemWeb in general) is to let people
>>format their data in XML however they want (and there's lots of
>>differing schemas out there...) and then provide a method for
>>"connecting" them if they refer to the same ontological abstraction.
>>This I believe what the RDF bindings for WSDL, WSDL-S, OWL-S, etc are
>>providing, and this is a *good* thing despite the differing details.
>>Think programming classs definition that lets one "hook" together all
>>your various Java classes, Python, and SQL stuff and say "this class in
>>Java, this class in Python, and this database table all refer to the
>>same person".
>>    
>>
>
>I think a "hook-together" mechanism is a great idea, but it
>doesn't have to be RDF and OWL that does it.  In my opinion,
>after having used them for the purpose, OWL and RDF are not
>a good fit for the data structures used in programming languages.
>
>  
>
>>And, as it must be pointed out again and again, XML does not provide a
>>formal semantics. It's a serialization format like ASCII - you don't
>>"reason" or "prove" things with just ASCII, do you?  Think of XML as a
>>representation format for data, and think of the SemWeb as a
>>representation format with a formal semantics for *what the data refers
>>to* .
>>    
>>
>
>I am familiar with that point and don't find it convincing.
>XML is not just like ASCII, for one thing; ASCII is at a lower
>level.  While it's true that XML lacks a formal semantics,
>in a sense that's just the lack of some agreed conventions
>for treating XML Schemas (or something else) as class definitions.
>
>Also, RDF has semantics in only a very limited sense.  It's
>what's needed "to provide a technical way to determine when
>inference processes are valid, i.e. when they preserve truth".
>What URIs refer to can vary with the model / interpretation.
>
>The RDF model theory says what it takes to be considered a model.
>It doesn't give you any model.  It's like having the definition
>of satisfaction for first-order logic plus the axioms for groups,
>but without (yet) any groups.  If you see http://...#dog, it probably
>means dog, but the model theory doesn't tell you that.  It has to
>be specified separately what that URI means, and often that will
>be done by natural-language text just as it is for Dublin Core
>"creator".  (In some cases - perhaps that dog has an OWL class
>definition - you get further before you have to resort of natural
>language, but the problem still occurs lower down.)
>
>There's also a question of how much reasoning is desirable.
>In order to check whether I can do the equivalent of a
>procedure call (which is what at least many invocations of
>web services are), should I have to use a description logic
>theorem-prover, or should I just have to do the sort of
>reasoning done in OO programming languages?
>
>-- Jeff
>
>  
>
Received on Friday, 25 November 2005 18:36:36 GMT

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