% notes from JC telecon 7/08/2003 % by Benjamin Grosof Discussion of DAML Rules strawman document sent by Benjamin Grosof participants: sandro benjamin ora harold said ian stefan mike dean pat would be good to include also: XML DTD for RuleML V0.8 "essential RuleML" examples -- e.g., that Said sent out to JC Sandro: would be nice to have a paragraph about what's surprising to those familiar with OWL, e.g., - LP semantics vs. FOL semantics Sandro: another section to have: test cases, e.g., for entailments - e.g., cf. OWL, that illustrate a group decision or agreement Mike: don't tie those decisions too closely to use cases Benj: should it be sprinkled throughout Mike: would have separate document for test cases consensus: yes, let's have a separate document for test cases and use cases, keep examples in the syntax & semantics document to be expository Sandro: but do we have a volunteer for an editor of separate document Mike: suggest we have one document to start, to keep it simple, then split it up later what's the goal for this document: - Sandro: would be nice to have a W3C Note Ian: early documents of DAML+OIL had single document, overview, what's it all about, what would you do with it, why do you want it; the whole thing can be relatively short, with a few key components: 1. handwave-y overview 2. reasonably brief worked examples illustrating the basic/key features of the language (in DAML+OIL, the syntax was specified here) 3. formal semantics with abstract syntax 4. formal concrete syntax Mike: yes, this is in line with what I'm thinking Benj: issue: What kind of expressiveness for V1? E.g., explicit equality (e.g., among URI's)? basic built-ins? Harold: explicit equality in undirected fashion is highly inefficient, LP community has basically given up on paramodulation and moved towards narrowing, which is a kind of non-ground term rewriting. Pat: I agree. Pat: Can handle equality via canonical forms, i.e., clustering around "equality hubs"; choice of what's canonical within any group of equal stuff could be different for different users, but it's OK as long as you can translate between them. Harold: please send any writeup you have about that Benj: how if at all would this change our spec of the rules language? Harold: we could omit the symmetry axiom Pat: we shouldn't tinker with the definition of what equality is, but simply permit systems to be incomplete in their inferencing Benj: I agree Ian: we can view this (directedness) as an implementation issue Benj: what should be the form of our spec of equality? E.g., should it be the four axioms from the note I sent, which Pat attributes originally to Liebniz? Pat: no, it should be directly be defined in the semantics as sameness in the model Benj: is that well worked out in the literature? Pat: yes some discussion about directed equality, with Harold and Pat Mike: it would be nice to have a test case for directed equality %% Benj: wrt syntax: what kind of syntax: XML, RDF, human-oriented string? two or all of those? Said: XML Mike: human-oriented string; tempted to use this as exchange syntax too Sandro: RDF Pat: worry about layering issues in putting it over RDF Ian: we can deal with serialization issues later Benj: most urgent seems human syntax for communication amongst ourselves and our document's examples, and XML syntax for being able to run in existing tools, then we can do RDF version later Sandro: how about using KIF Pat: official KIF Ian and Benj: we can keep this pretty simple, e.g., Prolog-y Benj and Mike: key issues are how to include URI's/Qnames, and unordered argument slots; also lists Harold's syntax (Prolog-like plus URI's/Qnames, and unordered argument slots) with : for Qnames, explicit prefixing of variables, say $ for rest variables, different symbol for typing besides ":" - action item: Harold and Said: will do a draft of that and present it at the next JC telecon %% Sandro: what format should the document itself have? consensus: let's do it in current stable version of XHTML %% Benj: any other issues we need to add to semantics, besides Horn LP semantics plus equality? E.g., basic built-ins or typing? %% issue: typing Mike: typing of literals and also of RDF types (and thus XML Schema) consensus: let's keep it simple to start Pat: getting data typing right is sometimes non-trivial, in OWL it took way more work than expected, eventually settled on a quite simple approach: "context-free", i.e., datatype is locally immediately associated with a (rdf:)literal, as opposed to being inferrable Mike: maybe rule language needs only to address typing of rules not of individuals Mike and Benj: a simple approach is to treat types as arity-1 predicates, i.e., as classes Pat: there's been a big debate about this in CommonLogic, e.g., should types instead be able to be checked immediately syntactically, modern inferencing engines are somewhere in the middle, have a special reasoner for type inferences (e.g., a RDFS subset of OWL), but some details of that are tricky, thus has become back-burnered in CommonLogic Benj and Pat: a lot of practical reasoners do use a simple sort hierarchy, e.g., in LP, Cyc, Snark - Pat: issue of overloading, tree-ness Benj: let's make it possible for those who do sorted systems to do it, but not get into it deeply ourselves in our spec consensus: extensibility to sortedness is thus an objective %%