Hi All --

Firstly, many thanks to Sandro et al for the Workshop report and minutes, and to Ben, Harold, Michael and Said for the Strawman powerpoint.

As Ben pointed out in the closing minutes of the workshop, there is a lot of good conceptual work from the logic programming community (well beyond the initial work on Prolog) that should inform any Web Rules effort.

In particular, we have an opportunity to "ride on the shoulders of semantic giants"  (or at least of tall people).

Reasoning with rules over the semantic web is going to be a conceptually complex process.  To bring order and accountability to such a process, we would do well to focus on semantics, authorability and understandability early on. 

There are at least three kinds of semantics to consider:

  101 --  tagging data and predicates with their real world types, as in xml or rdf

  102 -- model theory based semantics that say what *should* be deducible from
            a collection of rules and facts

  103 -- executable English sentences that document what we mean by our predicates

I think we all pretty much understand the 101 part. 

For 102, there is the question of *which* semantics.  The leading candidates would appear to be (a) stratified range-restricted datalog with negation [1], or (b) the well-founded semantics [2].  Note that (a) is two-valued -- true or false -- while (b) is three-valued -- true, false or unknown.  There are many successor papers to each of [1] and [2].

The need for semantics103 can be seen by reading the jena-dev and other SW-related lists.  There, one daily sees smart people getting thoroughly confused about the meanings of RDF and OWL constructs and reasoning processes when translated into English. 

In our work, we have fielded an online system [3] that meets the 103 need without getting deep into NL research.  However, the system depends on having a firm basis at the Semantics102 level.  Thus, this is more than 'syntatic sugar'  [4].  For example, a two-valued closed world semantics102 can support, at the semantics103 English level, an open world flavored predicate such as "so far as is known at the moment, flight 678 is on time".

So, here is a proposal for prioritization, as Harold has suggested.

A.  Add to the top of the "semantic layer cake'"a "rules authorability layer".  Perhaps just rename the FOL++ block in the strawman ppt .

B.  Rank the available Semantics102 candidates from the literature [1,2,...]

I hope all of this makes sense.  If anyone would like to set up a time to call us at (USA) 860 830 2085, I'll be glad to discuss.  Thanks in advance for comments on the list too.

                                -- Adrian


[1]  K. R. Apt, H. A. Blair and A. Walker, Towards a theory of declarative knowledge,
in J. Minker, ed., Foundations of Deductive Databases, pp 89-148, (Morgan
Kaufmann, Washington, 1988).

[2]  Van Gelder, A., K.A. Ross, and J.S. Schlipf. 1991. The Well-Founded Semantics for General Logic Programs. Journal of the ACM 38(3):620--650.

[3] Internet Business Logic, online at www.reengineeringllc.com

[4]  http://www.w3.org/2004/12/rules-ws/paper/19



INTERNET BUSINESS LOGIC (R)
www.reengineeringllc.com

Adrian Walker
Reengineering LLC
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Bristol
CT 06011-1412 USA

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