I think this is just going to happen time and time again, "RDF non-sense": "The W3C Working Group members argue SPARQL is a mixed mode language that does support OR, though they are calling it an "optional union". Frankly, I see no point in renaming something people understand to mean one thing. It gives me the impression the W3C want to be thought police and enforce a certain way of thinking.
On the practical side, many analysts happen to like OR disjunctions and would complain loudly. Of course, there are plenty of cases where users abuse the power and write deeply nested disjunctions. That is not a valid reason in my mind to avoid disjunction. It saves the user time and allows them to write simpler rules using disjunction. The W3C seems love RDF and wants the world to love it. Unfortunately, the current specification is a complete piece of junk. I hope RDF dies a quick and public death."
I declare...backward chaining suits me fine! "My two favorite declarative tools right now are Pellet and Prova, both of which are open source java SemWeb tools that are highly compatible with Jena, which recently got a bump to 2.3 with fairly complete SPARQL support. Pellet is an implementation of OWL-DL and some related description logic facilities by the Mindswap guys in Maryland, who have absorbed some of the l33t Kowari/Tucana guys, too (Tucana was recently picked up by Northrop, BTW)."
"Prova is a prolog-variant built on top of Mandarax. It is a very effective and fun medium for scripting of high-level relationships and operations. The integration of prolog unification, java types, java methods, and java exceptions is done very nicely, and yields fine code economy. There are some rough edges in the docs, but we are helping to get these worked out in the pretty soon."
I guess that means David W is l33t! :-)