This is a reply to a message sent some time ago. However, I think it
sufficiently important enough to clarify its content to justify a
response despite the tardiness. (01)
Roy Roebuck III wrote:
>I've used the following analogy when describing Topic Maps in relation to RDF
>and other "knowledge-management" technologies. --- Consider an organization
>to be like a "book", full of information, but not well organized, not highly
>navigable, and not searchable. Topic Maps provide the functional equivalent
>of a hyperlinked "index" (including concordance capabilities) to this
>'organization as a book", while technologies like RDF provided the functional
>equivalent to a "Table of Contents" to the book.
>
>RDF focuses on hierarchy and categorization/classification/taxonomy, while
>Topic Map focuses on associations/relations/networks/lattices. I believe
>that OWL provides both the "Table of Contents" and the "Index" to the subject
>being modeled. (02)
This characterization of RDF is likely to be misleading for most people.
Taxonomies are usually thought of as trees made up of branches which are
totally disjoint subtypes of the type node from which they branch. RDF
and RDFS have no way of specifying such disjointness nor is it assumed
(an rdfs:Class can be a subtype of more than one other rdfs:Class and
an individual can be typed by multiple classes as well).
Furthermore, RDF is based on a graph model which supports networks and
lattices. RDFS has a first class meta-element for relation, called
Property. RDF is not about categorization but rather about description.
It is RDF that provides URIs to identify any Resource in its universe;
OWL adds expressivity primarily for describing Resource types. It's OWL
that adds constructs which enable classification and much richer consistency
checking to the Semantic Web "stack". (03)
Contrary to what the above might lead you to believe, I am not a booster
for RDF. The above characterizations are just so off the mark, I wouldn't
want them to spread. (04)
Evan K. Wallace
(former participant in the W3C Web Ontology working group which developed
OWL and current chair of the OMG Ontology PSIG that is developing the
Ontology Definition Metamodel specification which includes a metamodel
for RDF(S))
Manufacturing Systems Integration Division
NIST (05)
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