# Review of Semantics Documnt

From: Jeff Z. Pan <pan@cs.man.ac.uk>
Date: Wed, 8 Jan 2003 17:24:45 -0000
Message-ID: <011d01c2b73a$e88b88c0$6bc65882@cs.man.ac.uk>

Cc: <www-webont-wg@w3.org>

Reviewer Name: Jeff Z. Pan
Affiliation: Computer Science Dept., University of Manchester

Document title:
Web Ontology Language (OWL) Abstract Syntax and Semantics (Editor's Draft 2
January 2003)

Editors:
Peter F. Patel-Schneider, Bell Labs Research
Patrick Hayes, IHMC, University of West Florida
Ian Horrocks, Department of Computer Science, University of Manchester

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Summary:

This document provides a high-level, abstract syntax for OWL/Lite and
OWL/DL, and gives a clear direct model-theoretic semantics to the languages.
Since RDF/XML is selected as the normative exchange syntax for OWL, a
mapping from the abstract syntax to RDF graphs is also provided, together
with the RDFS-compatible model-theoretic semantics.

This document was generally of very good quality. The structure is very
clear, and the work is solid and important. Most parts of the document are
relatively easy to understand.

The only part that is not so easy to follow is section 5.2. Most of the

**1. Something I don't quite understand:

- section 5.2, why does owl:complementOf have only-if, but not iff
characterization, while sameClassAs and disjointWith etc have iff
characterizations. I become wondering what will happen if we change e.g.
sameClassAs to only-if characterization, does the reasoning rely on the

**2. some typos:

- section 5.2, I(E) should be S_I(E), or atleast introduce/define I(E)
somehow like that in RDF MT.

- section 5.2, "RDFS domains and ranges" part, column 3 of row 1 in the
table, "CEXT" should be "EXT".

- section 5.2, "R_I contains elements corresponding to all possible OWL
descriptions and data ranges" part, in the sentence "The first three
conditions ... ", why "three", aren't there two? (It should be three if we
consider the third item of part **3.)

- Appendix B.1, first example line 4, is "value" missed in front of
"(ex:author ..."?

- Appendix B.1, second example line 2, is "intersectionOf" missed?

**3. minor bugs:

- section 5.2, "Some OWL properties have only-if characterizations", the
last rule of the second table, "if E is owl:oneOf ...", this is not common
portion of the semantics of OWL/DL and OWL/FULL, thus should be moved to
section 5.4. Also in this rule, it seems that "RI OR LV" should be "RI" or
"IOT" (in OWL/FULL they are the same), since LV is already a subset of RI.

- section 5.2, "Some OWL properties have only-if characterizations",the
fourth table, "y\in IOC" should be "y\in IOC OR IDC".

- section 5.2, "R_I contains elements corresponding to all possible OWL
descriptions and data ranges", if there exists l, a sequence of x1,...xn
over IOT OR LV, then there exist y with y\in CEXT(I(rdfs:Class)), <y.l>\in
EXT(I(owl:oneof)): I think this rule should be moved to section 5.4, and in
here (section 5.2) should be replaced by two, one for IOT and the other for
LV, otherwise if x1,...,xn are mixed objects/values, it will cause trouble
to OWL/DL.

- Appendix B.2, the three antecedent triples don't entail Susan is an
object, and friend is an individual property.

**4. Some suggestions:

- section 5.2 "Relationships between OWL classes", it is kind of weird to
have  two (or more than two) tables as conditions without any explanations.
Instead, it might be better if we explain that the relationships between OWL
classes may be divided into subset relationships (the first table) and
membership relationships (the second table).

- section 5.2 "Characteristics of members of OWL classes": it might be a
good idea to have some descriptions before the table. In general, some more
texts are needed to make section 5.2 easier to understand.

- section 5.3, second paragraph, "V'" includes VRDFS, while in section
5.3.2, the last sentence of second paragraph, "V'" is disjoint from VRDFS.
It might be a good idea to change the first one to "V".

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--

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Jeff Z. Pan  ( http://DL-Web.man.ac.uk/ )

Room 2.100                                     email: pan@cs.man.ac.uk
Department of Computer Science      Tel:+44 (0)161 275 6145
University of Manchester                   Fax:+44 (0)161 275 6204