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Re: abstract syntax and RDFS

From: Jim Hendler <hendler@cs.umd.edu>
Date: Tue, 21 Jan 2003 08:04:24 -0500
Message-Id: <p05200f05ba52f54bdfcd@[]>
To: Jeremy Carroll <jjc@hplb.hpl.hp.com>, Guus Schreiber <schreiber@swi.psy.uva.nl>
Cc: WebOnt WG <www-webont-wg@w3.org>

Jeremy, I really don't agree with most of the detail of the below 
with respect to the CR criteria you propose (although if we meet them 
I think we would have the privilege of being the WG with the most 
complete implementation report in the history of the W3C), but there 
is one thing I think we need to do first whatever the group decides 
-- that is, get to Last Call.   Let's do what we need to finish our 
documents and then deal with the issue of our CR/PR dates and needs.

At 9:27 +0000 1/21/03, Jeremy Carroll wrote:
>>The owl.wol file defines owl:Class as a subclass of rdfs:Class.
>>So this seems redundant to me, or are we not assuming owl.owl is 
>>always imported? The same holds for the other examples 
>>(owl:ObjectProperty is a subclass of rdf:Property, etc.).
>>Sorry if I misunderstand.
>I think it might be helpful if I explain where I am coming from ...
>- the syntax of OWL Lite and OWL DL is defined by these mapping rules
>- the semantics of OWL Lite and OWL DL are defined in terms of the 
>abstract syntax.
>- there is a lot of free choice in the exact mapping rules used 
>(syntactic options which do not present semantic difficulties). This 
>choice should be made motivated by various concerns.
>The principle goals of a syntax are:
>1: connection to the semantics - this is primary, the syntax must 
>not present unnecessary obstacles to arriving at the meaning of a 
>(we are a bit on a loser starting from RDF/XML but that's another story)
>2: ease of exposition
>    It must be possible to articulate what the syntactic rules are, 
>in a way is reasonably clear.
>3: clarity of error messages
>    A syntax is used in tools like an editor or a syntax checker.
>    A syntax is also used in any tool that can read OWL Lite and OWL DL.
>    At least some of these tools need to be able to output correct 
>and intelligible error messages on ill-formed input.
>4: ease of porting, interoperation with other syntaxes
>    I see DAML+OIL, RDF and RDFS as the targets here.
>This suggests the following syntactic concerns as CR exit criteria:
>+ OWL syntax checker:
>    at least two independently produced syntax checkers that:
>    - can be run in an OWL Lite or OWL DL mode
>    - at least one of which, when presented with a document that is
>      not OWL Lite can give clear and intellegible indications as to
>      why not.
>    - at least one of which, when presented with a document that is
>      not OWL DL can give clear and intelligible indications as
>      to why not.
>    - can be run in strict mode, conforming with the exact specification
>      (i.e. very unhelpful).
>+ OWL editor
>     at least two independently produced OWL editing environments that:
>     - can be run in OWL Lite or OWL DL mode
>     - in OWL Lite/OWL DL mode either prevent the user from creating
>       non OWL Lite/OWL DL files, or provide some assistance in fixing
>       syntactic problems related to belonging to the correct
>       sublanguage. (I personally doubt that a set of emacs macros can
>       achieve this satisfactorilly)
>+ OWL documents
>      The construction of enough OWL sample data,
>       e.g. two moderate sized OWL Lite ontologies, two moderate sized
>       OWL DL ontologies, two moderate sized OWL Full ontologies
>      The porting of at least two moderate sized DAML+OIL ontologies
>       into OWL.
>      The porting of at least two RDFS schemas into OWL Lite; in such
>      a way that interoperation between RDFS and OWL Lite is shown.
>      A strong preference that Dublin Core is one of these.
>Now, let's get back to the original question. Why do I want the 
>mapping rule for owl:Class to optionally redundantly specify that 
>the URIref is also an rdfs:Class?
>Answer, if it isn't in the mapping rule then any RDFS schema that 
>defines or uses an rdfs:Class is not part of OWL DL or OWL Lite. It 
>is semantically  neutral.
>The current rule that you must not use rdfs:Class or rdf:Property in 
>an OWL Lite document seems difficult to explain, and difficult to 
>justify and to present unnecessary problems in interoperation 
>between OWL Lite and RDFS.
>Therefore it should change; the change I propose is, as you noticed, 
>semantically vacuous; which is deliberate. It indicates that there 
>are no possible semantic problems in agreeing to it.

Professor James Hendler				  hendler@cs.umd.edu
Director, Semantic Web and Agent Technologies	  301-405-2696
Maryland Information and Network Dynamics Lab.	  301-405-6707 (Fax)
Univ of Maryland, College Park, MD 20742	  240-731-3822 (Cell)
Received on Tuesday, 21 January 2003 08:08:17 UTC

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