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RE: DAML+OIL: Questions & Improvements.

From: King . Dany <DKing@drc.com>
Date: Sat, 27 Jan 2001 22:42:12 -0500
Message-ID: <80090D89EF34D311B69F00508B2C6E4327C1E1@orl01.drc.com>
To: "'Ian Horrocks'" <horrocks@cs.man.ac.uk>
Cc: "'www-rdf-logic'" <www-rdf-logic@w3.org>
Ian,

> -----Original Message-----
> From: Ian Horrocks [mailto:horrocks@cs.man.ac.uk]
> Sent: Saturday, January 27, 2001 11:22 AM
> To: King . Dany
> Cc: 'Dickinson, Ian J'; 'www-rdf-logic@w3.org'; TeamXML
> Subject: RE: DAML+OIL: Questions & Improvements.
> 
> 
> Hi Dany,
> 
> On January 26, King . Dany writes:
> > Hello Ian,
> > 
> > Thanks for your comments...  I agree that RDF is a 
> meta-language; however
> > it's purpose is to describe resources on the web.  
> DAML+OIL, on the other
> > hand, is meta-language for defining ontologies.  DAML+OIL could be
> > implemented in a number of ways.  At the moment, the 
> DAML+OIL is being
> > implemented with RDF.  It is my understanding that the use 
> of RDF is for
> > syntax only, because the semantics of DAML+OIL differs 
> greatly from mere
> > resource description. Thus, the root DAML+OIL ontology 
> should contain the
> > primitives of the meta-language used to define it 
> (rdfs:Class, rdf:Property,
> > rdf:ID, etc.).  However, instances of DAML+OIL (ontologies 
> built using the
> > DAML+OIL meta-language and their resulting instances) 
> should only contain
> > DAML+OIL primitives (see question @@ in original email). 
> Although there is a
> > 1 to 1 mapping on many  of the DAML+OIL primitives to the 
> RDF primitives
> > (this is true only because RDF syntax is being used), there 
> is at least one
> > case which has no mapping: the concept of a class.
> 
> The thinking behind the use of RDFS is that it already has the basic
> elements of an ontology language - classes, properties, constraints,
> and subclass and subproperty relations - and that DAML+OIL should
> clarify (semantically) and extend (in some respects) what is there
> already. DAML+OIL tries to maximise backwards compatibility by using
> as much of RDFS as possible and only extending it where necessary. For
> example, DAML+OIL uses the RDFS subClassOf relationship to (partially)
> order the classes in an ontology. The advantage with this is that a
> DAML+OIL ontology is partly accessible to any agent that understands RDFS.

Backward compatibility is good.  The general concept makes sense.  However,
there are currently only 13 DAML+OIL class/property equivalences to
RDF/RDFS.  Is it not from these 13 classes/properties that the DAML+OIL
primitives were defined?  So, currently existing RDF tools will be able to
process and interpret the use of those 13 RDF/RDFS primitives.  But, there
are 34 DAML+OIL primitives: "equivalentTo", "sameClassAs", "samePropertyAs",
"disjointWith", etc. (Note: the DAML+OIL primitives were defined in name
only.  Specifications were provided for their functionality but for nearly
all, definitions were not. From which I infer, that RDF is incapable of
defining such specifications, and/or that the burden of interpretation of
the DAML+OIL primitives will be picked up by DAML+OIL
tools/compilers/processors.) Can currently existing RDF tools process and
interpret these DAML+OIL primitives? Syntactically, because DAML+OIL is
implemented with RDF, the answer is yes.  But semantically, because of the
undefined functionality the answer is no.  Even after DAML+OIL (and +
whatever else) has solidified and DAML+OIL tools are available, should RDF
tools be modified to interpret DAML+OIL?  Since DAML+OIL is but one use of
RDF, I don't think so. It appears to me that the vast majority of the
semantics of DAML+OIL is not supported by RDF or its tools.  Hence,
semantically speaking, DAML+OIL is not backward compatible with RDF.
Syntactically however, it is... mostly (discrepancies: 1. RDF is requires
acyclic subclass relations, DAML+OIL allows cyclic subclass relations; 2.
DAML+OIL requires one syntax for cardinality to avoid exposed content, thus
other equivalent and legal RDF syntaxes are illegal for DAML+OIL
cardinality; 3. RDF allows only one range restriction per property, DAML+OIL
allows multiple; 4. the "daml:collection" doesn't exist in RDF).  Therefore,
with such vast differences in semantics and a ever growing syntactic
divergence, how can backward compatibility be an issue?

> The reason for defining the daml equivalent classes and
> properties was simply to save users from having to use namespace
> prefixes (in which they fail anyway, unless the ontology is defined in
> the same namespace as the daml+oil language definition).

There is still at least one benefit to having the equivalencies... There
would only be one namespace prefix for DAML+OIL instead of three.  Why
should the user have to be concerned with knowing when to use "rdf", "rdfs",
or "daml" as a prefix?  For the sake of the tool builders, it is
understandable that the use of RDF/RDFS prefixes is helpful.  But after the
DAML+OIL tools are operational, shouldn't the use of the RDF/RDFS prefixes
be depreciated?
By the way, equivalences were not defined for "rdf:ID", "rdf:about", and
"rdf:resource".

Dan
Received on Saturday, 27 January 2001 22:45:35 GMT

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