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Re: comments on RIF BLD from OWL WG

From: Chris Welty <cawelty@gmail.com>
Date: Tue, 29 Jan 2008 10:28:44 -0500
Message-ID: <479F462C.6050903@gmail.com>
To: "Peter F. Patel-Schneider" <pfps@research.bell-labs.com>
CC: public-rif-comments@w3.org, "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>


Here are responses to your message "from the OWL WG" to RIF public comments on 
Nov. 2.  Feel free to forward to the owl-wg, I cannot post to it.

 > ** Comments on the Syntax

 > Why is the complex signature mechanism in this document, as the only
 > used language doesn't really need it?

Signatures are part of the general framework of RIF from which other
dialects are to be derived. This general framwork has meanwhile been split off
of the dialect specification, resulting in the FLD document.

 > Further, the signature mechanism
 > cannot capture the syntax of the BLD condition sublanguage, so it is not
 > even adequate for distinguishing between dialects.

This question is quite unclear.  The signature mechanism is intended to be used
for defining and extending RIF dialect semantics.  Can you be more specific?
What do you mean by the inability to "capture" the syntax and why it is relevant?

 > Why are there are three different kinds of atomic formulae (regular,
 > slotted, and frame)?  This could cause problems with OWL integration, as
 > it is not obvious which kind of formulae should be used for integration
 > with OWL.  In particular, frame formulae might be the target for OWL
 > Full and regular formulae the target for OWL DL.

The three kinds of formulae are related formally and, in fact, we expect frames
to provide a natural way to anchor the OWL integration work.  The others are present
because the RIF framework is intended to capture all the major types of atomic
formulas used in rule languages.

 > * Semantics of the RIF BLD Condition Sublanguage
 > The semantics is only for the RIF BLD Condition Sublanguage, not the
 > full RIF Condition Sublanguage.

At present we are specifying RIF-BLD.  Other dialects will be specified
separately and in due time.  The "Condition Language" distinction will
be removed in future drafts and the syntax & semantics merged into the
apprpriate BLD sections.

 > * Comments on the Semantics
 > The mappings for predicates are partial.  It seems that this means that
 > the truth value of some formulae are thus undefined, but no account is
 > taken of this in the later development of the semantics.

This has been fixed.

 > Why is a new treatment of data values needed?

The treatment is not new -- it is equivalent, but more uniform. It was chosen
for its uniformity, since the same mechanism can be used other RIF needs:
data types and other kinds of symbols (IRIs and local).

 > Why does the set of known
 > data types not include XSD data types like xsd:short?

It was decided to start with a subset of the data types.  There is no
technical reason to exclude xsd:short and others. They might be included in
the future.  It is also not clear why an exchange language needs to support
all the XML data types.

 > Why does there need to be a symbol space for IRI identifiers?  This may
 > cause problems with OWL integration.

This symbol space corresponds to RDF's resources. Which problem can it cause for 

 > The treatment of slotted formulae is unusual in that the predicates have
 > a direct map to their extension but the slot names are first mapped into
 > the domain.  This means that a=b implies that f[a->3] is equivalent to
 > f[b->3].

In what sense is it "unusual"? It is usual in F-logic, but can be prevented by 
signatures (in dialects).
To be elaborated upon in the followup draft.

 > * General Comments on the Condition Language
 > The language is very complex.  It appears to have been designed to
 > mirror several other languages.  In particular, the frame formulae
 > appear to have been designed to mirror F-logic.
 > The logic is not like RDF, as it is monomorphic and predicates are not
 > first mapped into domain elements.

This is intended to be changed in the next draft.

 >  The frame part of the logic is not
 > like regular frames, as the slot names are first mapped into domain
 > elements.

What is a "regular" frame?

 > * Notes on RIF-RDF compatability
 > Why worry about interpretations where IP is not a subset of IR?  This
 > only happens in simple entailment.  As there are already datatypes in
 > RIF why not just go to datatype-entailment?

It is at the moment not clear which entailment regime(s) will be useful for RIF. 
  It might be the case that we decide to use only D-entailment.  See also the 
second last paragraph in the 
[http://www.w3.org/TR/2007/WD-rif-rdf-owl-20071030/#Overview introduction].

 > The treatment of ill-typed literals appears to allow accidental capture
 > if the replacement IRI also occurs in the RDF graph.  For example,
 >    "abc"^^xsd:decimal ex:a ex:b .
 > RIF-RDF entails
 >    ex:a ex:b .

There was already general skepticism in the working group about using such an 
IRI encoding of ill-typed literals.  It was decided to remove this encoding, so 
that it is no longer possible to directly use ill-typed literals in RIF rules.
See also the example in 
[http://www.w3.org/TR/2007/WD-rif-rdf-owl-20071030/#RDF-Compatibility section 2].

Note that it is, however, not the case that RIF-RDF entailment matches RDF 
D-entailment when the set of rules is empty; see the example at the bottom of 

 > Note that rdf:type is not related to membership formulae (i#c) and
 > rdfs:subClassOf is not related to subclass formulae (c1##c2).  This does
 > not seem to be reasonable.

In the [http://www.w3.org/TR/2007/WD-rif-rdf-owl-20071030/ current draft] they 
are related; see 

 > * RIF-OWL Compatability
 > There was a section on RIF-OWL compatability in an earlier draft of the
 > document but it has been removed.
 > * Notes on RIF-OWL Compatability.
 > There is a question as to which part of the syntax OWL should map to.
 > There is also a question as to whether OWL syntax should map to RIF
 > facts.

The questions will be addressed by the recently established OWL-RIF taskforce.

Dr. Christopher A. Welty                    IBM Watson Research Center
+1.914.784.7055                             19 Skyline Dr.
cawelty@gmail.com                           Hawthorne, NY 10532
Received on Tuesday, 29 January 2008 15:29:16 UTC

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