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Review of Reference

From: Jeff Heflin <heflin@cse.lehigh.edu>
Date: Thu, 02 Jan 2003 17:27:24 -0500
Message-ID: <3E14BCCC.3BF464A7@cse.lehigh.edu>
To: WebOnt <www-webont-wg@w3.org>

Hello,

Here is my review of the Reference doc. This review incorporates
comments from my students, who I also asked to read it. I have divided
my comment into "Major comments" (which are those which I consider to be
most important and/or substantive) and "Minor comments" (where are
mostly syntactic errors or typos).


Major comments:
------------------
- You need to number at least one level of subsections and include them
in the table of contents

- In general the document does not serve its purpose as a syntax
reference very well. Ideally, I'd like to see the grammar for each
language construct. The RDF Schema is only helpful to those who already
know RDF pretty well. I'd like our potential readers to be able to use
this as a definitive document about what's valid syntax in the language
and what is not.

- Language structure, para. 3, "An OWL ontology consists of an optional
ontology element.": The element shouldn't be optional. If the person
want their document to be an ontology, it should have an ontology
element. Of course, they are free to define classes and properties in
other documents, and they may not define any classes and properties in a
document with owl:Ontology, but neither of these should be encouraged.

- Class elements, sameAs bullet: owl:sameAs when applied to a class DOES
NOT have the same semantics as owl:sameClassAs. owl:sameAs is a synonym
for sameIndividualAs which when applied to classes say they are the same
individuals and thus have the same properties, including e.g. the same
values for rdfs:label. owl:sameClassAs only means that the two classes
have the same extension (i.e., the same members) and says nothing about
what properties the two classes have in common.

- Enumerations: We need to discuss what form the enumerated elements can
take, i.e., any form of individual is applicable.

- Property restriction, "... possible to create restrictions that are
neither object restrictions nor datatype restrictions, but these
restrictions are not handled within OWL.": Is this statement true for
OWL Full? I don't think so.

- Property elements, subPropertyOf: Says "each containing a property
name." Must a subPropertyOf contain a property name, doesn't RDF allow
it to be anonymous Property class? Also, containing is too fuzzy a word
for a reference document.

- Property elements, samePropertyAs: Doc says "samePropertyAs element
asserts that P is equivalent to the named property." This could use some
clarification. In particular what instances are for properties, and also
to make it clear that meta-properties (properties of the properties are
not asserted to be equivalent when this is used.

- Property elements, last para. "A property is a binary relation that
may or may not be defined in the ontology." Did the WG ever discuss
whether or not it was legal to reference a class or property that wasn't
defined in the ontology? I certainly would not support this. It makes it
even easier for errors to creep into ontologies.

- The RDF Schema for OWL should be textually included in the document,
so that if people print it out, they get it as well

- The document needs to describe how data documents can use OWL
ontologies, and in particular, how to import them, i.e.:

<rdf:Description rdf:about="">
   <owl:imports rdf:resource="someont">
</rdf:Description>

Minor comments:
--------------------
- 2. Language structure, para. 1: This structure RDF format => This
structure RDF XML format

- Ontology elements, bullet 1: "Importing an ontology into itself is
considered a null action, so if ontology A import B, and B imports A,
then they are considered to be equivalent." => "Importing an ontology
into itself is considered a null action." (i.e., get rid of the so if
part; it's not helpful and I don't even think it's true)

- Objects and datatype values, para. 2: after " elements of owl:Class, a
subclass of rdfs:Class": Mention what makes owl:Class different from
rdfs:Class, i.e., in OWL DL it does not include rdfs:Class and
rdf:Property as members.

- Objects and datatype values, para. 1 & 2: At first it says "OWL
divides the universe into two disjoint parts. One part consists of the
values that belong to XML Schema datatypes. "  While at the middle of
the second paragraph, "OWL also allows the use of XML Schema datatypes
to describe (or define) part of the datatype domain." My concern is the
"part of". If XML Schema datatypes is part of the datatype domain, then
what is else?

- Class elements, enumeration bullet: mention oneOf here.

- Class elements, last sentence, "Notice that the first two elements
state necessary but not sufficient conditions for class membership. The
final four elements state both necessary and sufficient conditions.": It
may be helpful to further explain this in less mathematical/technical
terms than necessary and sufficient.

- Property restrictions, elements indicating the type of restriction, 
"To see why this is so, observe that the owl:allValuesFrom restriction
demands that all values of P belong to class P, and if no such values
exist,
the restriction is trivially true." Change "all values of P belong to
class P" => "all values of P belong to the specified class expression"

- Property elements, FunctionalProperty, "shorthand notation for the
owl:maxCardinality restriction of 1" add "(when applied to the class
Thing)" (since FunctionalProperty is global and maxCardinality is
local).

- Property elements, Warning at end, "If an owl:TransitiveProperty (or
any of its superproperties) is used in a cardinality constraint, then
class consistency is no longer necessarily decidable.": We need to
define what we mean by class consistency rather than just dropping this
term on the poor reader.

- Deprecation: in the comment of Automobile, change "sameClass" to
"sameClassAs"

- Appendix A: DatatypeRestriction and Datatype value look out of place,
since they are really syntactic tokens in the language.



-------------------------------------------------------------
Here are some additional comemnts on
http://www.daml.org/2002/06/webont/owl

- We should import the Dublin Core schema. i.e. add:
  <imports rdf:resource="http://purl.org/dc/elements/1.1/">
to the ontology header.

- replace Property tags with rdf:Property tags for sameAs, sameClassAs,
samePropertyAs, etc. (since there is no longer a Property synonym in the
owl namespace
Received on Thursday, 2 January 2003 17:27:27 GMT

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