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RE: fulfilment of my action of today <-- Rumblings on why we need classification terms in RIF (and why RDF's vocab should not be used)

From: Paul Vincent <pvincent@tibco.com>
Date: Wed, 15 Aug 2007 03:44:11 -0700
Message-ID: <8F4A4531BB49A74387A7C99C7D0B0E0502F0BCE9@NA-PA-VBE02.na.tibco.com>
To: "Chris Welty" <cawelty@gmail.com>, "Michael Kifer" <kifer@cs.sunysb.edu>
Cc: "RIF WG" <public-rif-wg@w3.org>

Out of interest (and apologies for the na´ve qu's): 
1. what would be an example rule here? 
eg: C1 is a subclass of C0 
[and by implication C1 inherits properties, maybe default values for such properties, from C0, and inherits method definitions, all subject to any intermediate subclass definition overrides]?

2. note that for a PR, as discussed in the call yesterday, the most likely equivalents would be:
- do a class membership query on some instance in a rule condition [not really a subclass test as class relationships are metamodel constructs]
- allocate an instance to some new class [not supported in most PR engines due to their Java object model base]

The above might explain why for the PR community the question on whether RIF supports this construct is somewhat irrelevant. I can't think how a PR translator would handle such a construct without recreating/simulating an OO model semantics dynamically or getting into code generation...  

[My 2cents contribution is that RDF vocab should only be used if RDF is the only "rule language / data model" requiring this feature OR RDF vocab is a sufficient abstraction of all "rule language / data model"s requiring this feature].  

Paul Vincent
TIBCO | ETG/Business Rules 
> -----Original Message-----
> From: public-rif-wg-request@w3.org [mailto:public-rif-wg-request@w3.org]
> On Behalf Of Chris Welty
> Sent: 15 August 2007 02:26
> To: Michael Kifer
> Cc: RIF WG
> Subject: Re: fulfilment of my action of today
> Michael Kifer wrote:
> > Rumblings on why we need classification terms in RIF
> > (and why RDF's vocab should not be used)
> > ===================================================
> >
> > Two issues: whether we should define facilities for expressing some data
> > model stuff and whether we should use rdfs for this.
> >
> > Rationale:
> >    If we do not have such constructs then everybody will be inventing
> their
> >    own. People will not be able to specify any part of their data model
> in RIF
> >    which will reduce the usefulness of RIF as an exchange language.
> >
> > Why it is not good to use RDF's facilities to define class hierarchies.:
> >    RDF is a foreign language whose semantics is burdened with non-
> standard
> >    things. For instance, subclass is reflexive.
> >
> >    This is bad because not every language out there uses reflexive
> subclasses.
> >    For instance, if we map, say, FLORA-2's subclass relationship to
> RDFS's then
> >    in the translation (RIF) the query whether foo is a subclass of foo
> will
> >    say "yes" but in FLORA-2 it will say "no".
> </chair>
> No, no - translating flora2:subclass into rdfs:subclass would be
> incorrect, because they have different semantics.  For me, this is the
> stronger point in favor of rif:subclass - since so few systems use the
> rdfs semantics for subclass, very few systems when translating into
> RIF would use it in their translations.
> Same for below.  You shouldn't translate ilog:subclass into
> rdfs:subclass.  So, in fact, as far as we know, only rdfs based
> systems would ever use rdfs:subclass when translating through rif, and
> everyone else would have to invent their own.
> <chair>
> >
> >    Let's look at some other examples, like ILOG. From my limited
> experience
> >    with it, I remember that it uses Java as its data model. So, suppose
> >    there is a class foo in ILOG, which comes from Java. An ILOG set of
> >    rules must not derive "foo sub foo" because this is not true in the
> data
> >    model. However, it we translate Java subclass relationship into
> >    rdfs:subclassOf then the resulting RIF translation should generate
> "foo
> >    sub foo". (In truth, as I recall, ILOG does not have "sub" in the
> heads
> >    of the rules, but it is easy to imagine that next year ILOG is
> extended
> >    with something like a query facility. Then their stock will plummet
> >    because their rule sets will not be faithfully exchangeable through
> >    :-)
> --
> Dr. Christopher A. Welty                    IBM Watson Research Center
> +1.914.784.7055                             19 Skyline Dr.
> cawelty@gmail.com                           Hawthorne, NY 10532
> http://www.research.ibm.com/people/w/welty
Received on Wednesday, 15 August 2007 10:44:27 UTC

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