W3C home > Mailing lists > Public > public-rif-comments@w3.org > September 2008

Re: comments on the BLD proposal

From: Chris Welty <cawelty@gmail.com>
Date: Tue, 23 Sep 2008 10:22:01 -0400
Message-ID: <48D8FB89.3000204@gmail.com>
To: Alexandre Riazanov <alexandre.riazanov@gmail.com>
CC: public-rif-comments@w3.org


Thank you for taking the time to provide us with comments. Some responses below.

Alexandre Riazanov wrote:

 > Hi list members,
 > I would like to add a few comments/questions on the BLD spec.
 > My interest in RIF is mostly driven by my implementation work, and in
 > particular by my current interest in using expressive KBs in relational
 > databases. I am considering using RIF BLD as one of the input languages
 > in a query answering system. This is a prelude, just to describe
 > my angle of view on the subject.
 > (1) First of all, I would like to say a word in support of the inclusion of
 > (RHS) equalities.
 > This is one of the features that makes RIF BLD useful and interesting for my
 > work. Without it, it would be a rather weak alternative to, e.g., SWRL. Perhaps,
 > my case is not unique. I also have some practical experience with knowledge
 > engineering with FOL-based formalisms, and one of the lessons is that without
 > equality, possibly restricted, it can become quite painful.

Thank you for this feedback. It is helpful.

 > (2) The current spec of the frame semantics is really confusing me.  The
 > condition on I_{frame} (in 3.2) creates a very strong
 > impression that o[a->b a->b] will not be equivalent to o[a->b] and, in
 > general, o[a->b c->d] will not
 > be equivalent to o[a->b] & o[c->d]. However, in 3.4 TVal_I on frames
 > respects the latter property.

The semantics makes it clear that these two are equivalent: Section 3.4, Item 6. 
We have now also added a mention of this property earlier in the document to 
preempt the wrong impression that one may get from reading the earlier sections.

 > (3) Use case 4.2 in http://www.w3.org/TR/2008/WD-rif-ucr-20080730/ uses
 > frames as (individual-valued) base terms.
 > The BLD spec does not seem to provide either syntax or semantics for such
 > use. Does it mean that such use was
 > considered initially but didn't make it to the spec?

The syntax and semantics do specify individual-valued frames, one of their most 
obvious uses on the semantic web is for RDF triples. What leads you to believe 
that the syntax or semantics are not provided? Or perhaps you mean something 
different by "(individual-valued) base terms".

e.g. the RDF triple

<http://ex.com/john> <http://ex.com/uncleOf> <http://ex.com/mary>.

can be written in the frame syntax as

<http://ex.com/john>[<http://ex.com/uncleOf> -> <http://ex.com/mary>]

where <xxx> is a shortcut for xxx^^rif:iri.

 > (4) In general, it would be extremely helpful (to me as an implementer) to
 > see a reference translation to FOL.
 > IMHO, the standard would be the right place for it.

By "reference translation to FOL" do you mean to take a set of BLD Formulae and 
translate them to FOL sentences? Or a logical embedding of the semantics of BLD 
in FOL?

 > (5) Minor thing: isn't External(c) a well-formed (base) term when c is a
 > constant?

No, See Section 2.2, Item 8. External is meant to be an anchor for an external 
function call, so External(c) is not a term, but External(c()) is.

 > Thanks in advance for any help on (1)-(4).

 > Finally, thanks to the BLD team for doing an overall good job and good luck
 > with passing the standartisation formalities!

Thank you.

Received on Tuesday, 23 September 2008 14:22:39 UTC

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