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   equivalentTo vs. XSLT

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Miles Sabin wrote:
> Paul Prescod wrote,
>>I would define the mapping _as_ a RDF/DAML(OWL) assertion using
>>DAML's (OWL's) equivalentTo relationship.
> Maybe I should have said transformation rather than mapping.
> I'll try again: once you've defined an executable transformation (eg. 
> using XSLT), what useful job is there left for RDF/DAML/OWL to do?

Probably none. But I wouldn't define an executable transformation in an 
XSLT program when I could define a declarative mapping in a single line 
of OWL.

First, the XSLT is Turing complete. That means that if you send an agent 
onto the Web to find an XSLT that translates ebXML into BizTalk, you 
have no idea what computational resources you are committing to run the 
transformation it finds. You can't even kill the process with confidence 
when it runs in an "unreasonable amount of time" because perhaps it was 
just one second away from completing the task. So you set some arbitrary 
runtime limit and take your chances. I *believe* that the computational 
properties of semantic web reasoners are more predictable. But I am not 
a computational logician so I could be wrong on that.

Also, there are issues around security and analysis of Turing-complete 
programs versus declarative specifciations. And serious optimization 
issues! So overall, I see the OWL route as being more reliable, secure 
and performant.

Second, the XSLT specification has weak support for handing off from one 
XSLT to another on a very granular (per-element) basis. Consider:



Wished-for Output:


I need to be able to switch mapping specifications's midstream from 
some-ns->my-ns to your-ns->my-ns. I'm having a hard time envisioning how 
I would do this in XSLT, but I think it is standard in logic languages. 
(Prolog calls it unification, but I think the Prolog algorithm is 
probably more powerful than is needed for OWL)

Third, I've never heard of anybody composing XSLTs that were developed 
entirely independently except by building a pipeline where the document 
is processed by one and handed off to another. What does the XSLT for a 
single element daml:isEquivalentTo look like? I'd guess it is something 
like an identity transform plus the single rule. Alternately you could 
use the precedence functionality and some kind of stylesheet 
concatenation but I don't think that the managing of precedence and 
scoping in a distributed fashion will work!  My perhaps faulty 
understanding is that it would be relatively easy for a processor to 
automatically go through many levels of renaming in OWL whereas in XSLT 
this would probably require some very tricky XSLT programming.

Fourth, it is much easier to use OWL as it was intended to be used than 
to chain-gang XSLT into the job. XSLT is not even designed to be a 
"general-purpose transformation language" much less a semantic mapping 

  Paul Prescod


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