I was surprised to learn that RDF reasoning appears to be very restricted, as in:

".

Surely, for RDF to function as useful service-finding glue in the Semantic Web, it should at least support discovery of resources by being able to walk arbitrary depth first- and second-order hierarchies/ontologies ?

Ah, I hear you say, but the inferencing needed can be undecidable, or at best inefficient.

Not so ! It's been known for a number of years that a form of datalog augmented with negation-as-failure has efficient, terminating, sound and complete inference methods.

There's a rather formal paper about this: Backchain Iteration: Towards a Practical Inference Method that is Simple Enough to be Proved Terminating, Sound and Complete. Journal of Automated Reasoning, 11:1-22, 1993. (Yes, these results have been around for a while !)

On the less formal side, here's a little example showing the kind of thing one would expect for really useful Semantic Web inferencing. The notation is that of the

Example:

1) Table heading:

=================================================================

2) Populate the table

=================================================================

sibling family

marriage family

family the class of all relationships

that-relationship2 is a specialization of some-relationship3

------------------------------------------------------------

that-relationship1 is a specialization of that-relationship3

that-relationship is a specialization of some-higher-relationship

---------------------------------------------------------------------------

that-person is related through that-higher-relationship to that-other-person

5) Provide some facts

=====================================================================

Fred marriage Jane

Fred sibling John

=====================================================================

Fred family Jane

Fred family John

Fred marriage Jane

Fred sibling John

Fred the class of all relationships Jane

Fred the class of all relationships John

sibling is a specialization of the class of all relationships

----------------------------------------------------------------

Fred is related through the class of all relationships to John

sibling is a specialization of family

family is a specialization of the class of all relationships

--------------------------------------------------------------

sibling is a specialization of the class of all relationships

One of the interesting things one can explore using this notation, is how to write the English phrasing and logic to avoid traps like John Sowa's famous example

So, this also begins to address the capture of English meanings in a form suitable for computation.

Hope this helps. All comments gratefully received. -- Adrian

PS: If your screen does not show monospace fonts, the above tables may be misaligned -- apologies.

Adrian Walker

www.reengineeringllc.com

PO Box 1412

Bristol

CT 06011-1412 USA

adrianw@snet.net

Phone: USA 860 583 9677

Cell: USA 860 830 2085

Fax: USA 860 314 1029