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Re: ISSUE 5.19 proposal to resolve

From: Jim Hendler <hendler@cs.umd.edu>
Date: Thu, 21 Nov 2002 11:47:13 -0500
Message-Id: <p05111707ba02bb3c5f5c@[]>
To: Guus Schreiber <schreiber@swi.psy.uva.nl>, WebOnt WG <www-webont-wg@w3.org>

At 12:16 PM +0100 11/21/02, Guus Schreiber wrote:
>SSUE 5.19 - Classes as instances
>I propose to resolve this issue in the following way:

this works for me

>[NOTE: Changes are marked with tags <add> and <del>, resp. standing
>for add or delete this piece of text.]

But I have some suggestions for the below

>OWL is in fact a set of three, increasingly complex languages.

For political as well as technical reasons I think it is VERY 
important that we as a group try to never
  i. Call this three langauges (they are named subsets of ONE language 
called OWL) - this is important because we are chartered to create 
one langauge only
  ii. use the term "complex" and OWL in the same sentence -- DL isn't 
more complex to use than LITE or less complex than Full - we designed 
these based on functional needs and guesses as to implementation 
complexity and implementor needs.  Also, users may construe "complex" 
to mean hard to use, as opposed to computationally complex (i.e. OWL 
Full is not harder to use than OWL Lite, but it could have 
computational ramification)
  iii. there are a large number of people in the world who think DL 
means "digital library" - I'd like to suggest the first use of OWL DL 
in each document needs to make it clear DL means Description Logic, 
not Dig Lib.

In light of these two things, I would like to suggest the following 
wording as an ammendment to Guus' proposal

replace the line "OWL is in fact..." with:

The OWL langauge provides two specific subsets that we believe will 
be of great use to implementors and language users.  OWL Lite was 
designed for easy implementation and to provide users with a 
functional subset that will get them started in the use of OWL.  OWL 
Description Logic (OWL DL) was designed to support the existing 
Description Logic business segment and to provide a language subset 
that has desirable computational properties for reasoning systems. 
The complete OWL language (called OWL Full to distinguish it from the 
subsets) also contains some powerful features for users that are 
available in many database and knowledge representation systems, but 
which violate the constraints of description logic reasoners.  OWL 
Full and its two language subsets have been designed for maximal 
compatibility with RDF and RDF Schema

>* Owl Lite has been defined with the intention of creating a simple
>   language that will satisfy users primarily needing a classification
>   hierarchy and simple constraint features. For example, while it
>   supports cardinality constraints, it only permits cardinality values
>   of 0 or 1. For these reasons, it should be simpler to provide tool
>   support for Owl Lite than its more complex relatives.
>* OWL DL includes the complete OWL vocabulary, interpreted under a
>   number of simple constraints. Primary among these is type
>   separation. Class identifiers cannot simultaneously be properties or
>   individuals. Similarly, properties cannot be individuals. OWL DL is so
>   named due to its correspondence with description logics.
>   <add>
>   OWL DL is expected to be supported by reasoning tools based on
>   description logic.
>   </add>
>* OWL Full includes the complete OWL vocabulary, interpreted more
>   broadly than in OWL DL, with the freedom provided by RDF. In OWL
>   Full a class can be treated simultaneously as a collection of
>   individuals (the class extension) and as an individual in its own
>   right (the class intension).
>   <del>
>   Another significant difference from OWL
>   DL is that a DatatypeProperty can be marked as an
>   InverseFunctionalProperty. These are differences that will be of
>   interest to the advanced user. This document does not describe the
>   use of these features.
>   </del>
>RDF users "upgrading" to OWL should consider whether they require OWL
>Full. This decision mainly depends on how much they want to keep using
>the metamodelling facilities of RDF Schema (i.e. defining classes of

I like that sentence, but...

>  The price you have to pay for OWL FULL when compared to OWL
>DL is that reasoning support is less predicatable. For more
>information about this issue see the <ref>semantic document</ref>.

...i nstead of being more predictable (what is unpredictable about a 
database key?)  Can we say instead something like

When using OWL FULL, compared to OWL DL, the language user is not 
necessarily provided with the computational benefits of Description 
Logics, which are desirable in many applications.

- basically, it is important that our documents don't say "Don't use 
Owl Full" because we run the risk of that getting thrown back to use 
when we try to go to a proposed recommendation (and that can cause us 
to have to revisit Lite, DL and everything else as well)

>When we introduce constructs that are only permitted in OWL DL or OWL
>Full, they are marked by "[OWL DL]" <add>resp. [OWL Full]</add>.
>Design for Use

I like this

>These issues are certainly for the more advanced ontology builder, and
>are not addressed in this document further.

agree that should be deleted - nice catch Guus.

>The point of this discussion is to note that the development of an
>ontology should be firmly driven by the intended usage. These issues
>also underlie one major difference between OWL Full and OWL DL. OWL
>Full allows the use of classes as instances and OWL DL does not. The
>wine ontology is designed to work in OWL DL, and as a result
>individuals like FormanChardonnay cannot simultaneously be treated as

I like this a lot - we might also consider putting on a web page 
somewhere (and linking here in our final document) a copy of the wine 
ontology with the FormanChardonnay example in it -- in fact, if we do 
accept a MIME keyword for DL v. Full v. Lite -- this would be a great 
example of that


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 Thursday, 21 November 2002 11:47:20 UTC

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