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[ALL] ODM Chapter review

From: Gary Ng <Gary.Ng@cerebra.com>
Date: Mon, 16 Jan 2006 03:25:55 -0800
Message-ID: <D3824B3639761949B599477A08C6A0180119E536@wyoming.ad.networkinference.com>
To: "SWBPD list" <public-swbp-wg@w3.org>

Elisa,

Sorry for the delay in sending these out. I took some extra time to read
it more carefully.

I have mainly focused on the OWL Chapter of [1], with some look ups into
the DL and RDF Metamodel chapters. The original reference to the doc is
at [2].

The OWL descriptions are accurate. I believe it has covered all OWL
constructs with minor quibbles. See "Quibbles" below with minor change
suggestions.

Recap: Base on the OWL abstract syntax, the metamodel covers all
language elements of OWL (OWLBase). The base model is a minimally
constraining specification. The sub-language variants are achieved per
application/vendor by constraining the usage of the elements, provided
as additional contraint packages. The OWLDL and OWLFull Constraints
Package have yet to be defined and I understand Peter Patel-S and Bijan
are helping to define those. 

Comment: Generally I find the interaction between RDF Document, OWL
Graph, RDF and OWL statements, together with OWL Universe, needs some
clarification. 

My concern can be summarized in the following questions, I find that the
answers are probably implied within the text, but I haven't found
satisfactory answers by myself and I need some help:


1. It seems OWL Universe, OWL Statements and OWL Graph are meant to be
derived objects that tool vendors are to support? No end-users will need
to explicitly specify them?


2. In 12.2.2: "As shown in Figure 14, an OWL ontology consists of a
collection of facts, axioms, and annotations, defined in terms of zero
or more RDF graphs and statements."

     Can statements made in RDF that represent OWL Expressions readily
translatable into OWLBase constructs? Can a resource graph specified in
the RDF profile be readily usable as an OWL instance graph? 

     From the other direction, RDFGraph contains RDF Statements.
OWLGraph is a subset of RDFGraph. Not all graphs are valid OWL Graph.
But does this mean that all OWL Expressions are also RDF Statements,
just like the relationship between RDF and OWL syntax? Need to clarify
that whether axioms and expressions made using OWL Metamodel has an
equivalent RDF Statement form just like the language. 

     But if the OWL Metamodel is based on the abstract syntax, which
means it does not necessary correspond to the RDF syntax for axioms,
which in turn would mean the OWL Ontology contains RDF Graphs + some
objects which can only be accessed through OWL Universe?


3. There seems to be two ways to specify an RDF triple? 

     One is to use a Statement stereotype, the other is to literally
associate one object to another with a link. The former allows
reification, and associate the statement with a graph, the latter
doesn't, and the fact that it becomes a statement is actually implicit.
Or is it the case that all triples must be specified through a statement
object with 3 links to subject, predicate, object explicitly, such that
reification and or named graphs can be specified?


4. Not really about the OWL MetaModel, but will we expect a rewrite of
the DL MetaModel (Appendix C)? What is expected to be done with it? It
looks like it still needs a lot of work.
 

============================ Quibbles ============================

Naming consistency: Suggest the names RDFGraph (for RDF) and
OWLStatement (for OWL) rather than Graph (for RDF) and Statement (for
OWL). Thus it is clear that there are: RDFGraph, RDFStatement, OWLGraph,
OWLStatement.

12.3.6 Individuals

SameIndividual and DifferentIndividual with associations sameIndividual
and differentIndividual have not been introduced before or anywhere else
in this chapter.

12.3.11 OWLDataRange

OWL DataRange can also be the rdfs:range of a Property but is missing
here. It is certainly not in the RDF Metamodel and thus should be
included here. 


12.3.13 RDFProperty

rdfs:domain and rdfs:range of property is covered in the RDFMetamodel
and is not covered here. In the spirit of completeness, perhaps a
pointer here to section 11.5.1 where they are described would be good.
Since they are also an integral part of OWL.


12.4 OWLBase Property

Under the meta class Property, the siblings specified here are:
FunctionalProperty, DatatypeProperty, ObjectProperty; Under
ObjectProperty, there are InverseFunctional, SymmetricProperty, and
TransitiveProperty.

I thought in OWL-Full DatatypeProperty may be InverseFunctional? The
organization certainly suggests that if it is inverse functional, it is
automatically object property, which is the case in DL. I went to
checked the webont reference:

   "NOTE: Because in OWL Full datatype properties are a subclass of
object properties, an inverse-functional property can be defined for
datatype properties. In OWL DL object properties and datatype properties
are disjoint, so an inverse-functional property cannot be defined for
datatype properties. See also Sec. 8.1 and Sec. 8.2."

(thinking aloud here...) So to create an inverse functional Datatype
property for OWL Full ontology from this meta model, one will have to
declare that property as both inverse function and as datatype. As
inverse functional prop is in turn an object property... the prop is
both a datatype and object property => which is consistent with RDF and
OWL-Full semantics. 

Granted. No issue. But perhaps to include some explanation to reassure
the reader that the semantics is correct with reference to WebOnt
reference?


12.6 Datatypes

Perhaps to explicitly mention that the OWL's notion of unsupported type
is automatically handled too? 

Doesn't need much description, as TypedLiteral and the RDFDatatype are
already described in the RDFMetaModel. Again, this is more like just
covering all OWL constructs like a checklist in this chapter rather than
just leaving it implied in the TypedLiteral section. 


12.2.3 RDFSLiteral

This section seems out of place and interrupted the flow. Perhaps move
to before or after 12.3.15 TypedLiteral?


12.3 Class descriptions

The alphabetical ordering of the sections on various annonymous classes:
"ComplementClass, Enumerated, Intersection, Restriction, Union", could
perhaps be arranged from simple (complement, intersection, union) to
complex ideas (restriction)? It was slightly interrupting reading
Intersection, then a detail long Restriction section, then back to
Union, which carries similar content to Intersection.


Typos
-----

12.1

    "Vendors who are interested in supporting OWL Lite would simply use
only the relevant constructs from the base package and tighted a few
constraints from the OWL DL package, as required."

Change "tighted" to "tighten" perhaps?


[1] http://www.omg.org/cgi-bin/doc?ad/05-09-08.pdf
[2] http://lists.w3.org/Archives/Public/public-swbp-wg/2005Nov/0174
Received on Monday, 16 January 2006 11:25:03 UTC

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