From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 05/13/05
I have a number of comments and questions concerning the document "Semantic
Web Services Language (SWSL) - Version 1.0". Most of these questions have
to do with the SWSL-Rules language.
Note that this is by no means a complete catalog of my concerns concerning
the document. Answers to these questions, particularly my fundamental
concern about semantics, may give rise to many other concerns.
Section 2.14
I am disappointed that the semantics for SWSL-Rules is not included in this
document. Pointing to external documents is not a substitute. I believe
that the external documents do not provide a semantics for the various
SWSL-Rules subsets. I cannot find any transformation to define the
Courteous layer in Grosof2004a. VanGelder91 does not provide a semantics
for the = and != operators. Without semantic definitions, it is hard to
determine just what is going on in the language.
Section 2.2
Is there any difference between f and f() as first-order atomic formulae?
The unification (=) and disunification (!=) operators are not appropriately
handled. First, what does "identical" mean here? Is it before or after
prefix expansion, for example? Second, "substitution" has not been
defined. Third, what is the scope of the subsitution? For example,
consider
p(?x) = q(f(?y)) and p(f(?x)) = q(?y).
And/or formulae are ambiguous. Consider
p1 and p2 or p3
Is this the conjunction of an atom and a disjunction or the disjunction of
a conjunction and an atom?
Section 2.3
Any appeal to semantically-related notions (like "equivalently") is suspect
here, as no semantics has yet been defined. This is particularly true for
illegal syntax.
I don't understand the stated allure of Horn rules. Couldn't I make a
similar statement about arbitrary first-order formulae being independently
characterized by entailment, models, and deductive consequences? How is
this in any way less desirable than being characterized by entailment,
a minimal model, and deductive consequences?
Section 2.4
The appeal to semantic reductions is not appropriate here. First, no
semantics has been given yet. Second, which semantics is to be used?
Section 2.5
No syntactic characterization of the extended syntax for this layer is
given.
Transformations into a syntax which is not defined do not provide useful
information.
Section 2.6
There is no definition of "equivalent" to use here, nor is the syntax
legal.
Without any proofs that the transformations preserve any useful
characteristics of the formulae, they should be treated very suspiciously.
Peter F. Patel-Schneider
Bell Labs Research
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