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Review of Semantics Documnt

From: Jim Hendler <hendler@cs.umd.edu>
Date: Wed, 1 Jan 2003 17:36:58 -0500
Message-Id: <p05200f4eba39161ea864@[10.0.1.3]>
To: webont <www-webont-wg@w3.org>

Review of 
http://www-db.research.bell-labs.com/user/pfps/owl/semantics/  31 
Dec, 2002.

Note - I do not consider myself qualified to handle the technical 
model theory, and therefore these comments confine themselves to the 
textual descriptions in the document.

Note to WG (not to editors of this doc) - lots of brownie points for 
anyone who implements the mapping from the abstract syntax to the RDF 
graphs as described in section 4!


Summary:with the exception of the one meta-comment below, I thin the 
document is in good shape and I have only minor typographical comments


meta-comment: the document is not consistent in its treatment of OWL 
DL v. OWL Full - this is okay since it is mostly about DL, but makes 
some of the text uneven because sometimes it says things like "cannot 
be translated into an OWL/DL graph" to mean that something is in 
Full, but not DL, but othertimes it says things like "OWL Property 
Axioms " to mean specifically the OWL DL ones (i.e. maintaining the 
separation of data and object types).  The editor should go through 
the document and try to be more consistent, and probably should add a 
comment near the top saying something like "unless otherwise 
indicated, in this document "OWL" will be used to denote the DL 
subset of OWL" and explaining why-- this might be done simply by 
promoting the paragraph

>The abstract syntax here is less general than the exchange syntax 
>for OWL. In particular, it does not permit the construction of 
>self-referential syntactic constructs. It is also intended for use 
>in cases where classes, properties, and individuals form disjoint 
>collections. These are roughly the restrictions required to make 
>reasoning in OWL be decidable, and thus this abstract syntax should 
>be thought of a syntax for OWL/DL.

to section 1.2 and giving it a heading, so as to emphasize it (and 
make it so people who skip to a middle section from the index cannot 
as easily miss this comment)


1) section 1.1  Differences from DAML+OIL reads:

>The only substantive changes between OWL and DAML+OIL are
>
>     * the removal of qualified number restrictions, per a decision of WebOnt;
>     * the ability to directly state that properties can be 
>symmetric, per a decision of WebOnt; and
>     * the absence in the abstract syntax of some abnormal DAML+OIL 
>constructs, particularly restrictions with extra components.
>

but of course that is no longer true.  This is true of OWL DL, not of 
"OWL" - and this section should probably also list the changes for 
OWL Full (i.e. eases separation restrictions) - the introdcution 
doesn't mention Full v. DL at all and it should (which is easily done 
by just mentioning it and providing a forward pointer to section 5.4 
and/or A.2 as necessary.

2) section 3 - Direct M-T semantics - (tiny style point) first 
sentence is hard to parse (esp. with misplaced "Section 5" words) 
maybe make it

This model-theoretic semantics for OWL goes directly from ontologies 
in the abstract syntax to a standard model theory. Thus is simpler 
than the semantics for RDF graphs, described in Section 5, which is 
based on a vocabulary extension of the RDFS model theory (Add 
citation link).



3) The following sentences from section 3 is technically fine, but 
some what odd

>The semantics here starts with the notion of a vocabulary, which can 
>be thought of as the URI references that are of interest in an OWL 
>ontology. It is, however, not necessary that a vocabulary consist 
>only of the URI references in an OWL ontology.

maybe reqord to make clearer (I'm okay leaving as is, but it might be improved)

4) near end of section 3 it says:

>An Abstract OWL ontology entails an OWL axiom or fact if each 
>interpretation of the ontology is also an interpretation of the 
>axiom or fact. An Abstract OWL ontology entails another Abstract OWL 
>ontology if each interpretation of the first ontology is also an 
>interpretation of the second ontology

are these "if" or should they be "if and only if" (in particular for 
the second one)

5) Section 5.1, second paragraph says

>In the more free-wheeling style, called OWL/Full here,

delete the word "here"


6) Section A.2 claims to be a "Poof Sketch" - an amusing typo but it 
probably should be fixed.

7) I'm not opposed to Appendix B, but in my mind it isn't of much 
use, could be deleted
-- 
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)
http://www.cs.umd.edu/users/hendler
Received on Wednesday, 1 January 2003 17:40:07 GMT

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