Bronze from anear, by gold from afar? points to Semantic Web Architecture: Stack or Two Towers? "Features such as closed world assumption and negation as failure (NAF) can be supported by powerful query languages—queries already have a closed world flavour (because distinguished variables can only bind to named individuals), and it is natural to extend this with NAF by way of query subtraction (e.g., the answer to the query “faculty(?x) and NAF professor(?x)” can be computed by subtracting the answer to the query “professor(?x)” from the answer to the query “faculty(?x)”). These features are already supported in query languages such as SPARQL [14] and nRQL [8] (the query language implemented in the Racer system). Moreover, recent work on integrating rules with OWL suggests that future versions of this framework could include, e.g., a decidable subset of SWRL, and a principled integration of OWL and Answer Set Programming [5, 12, 13].
On the other hand, adopting Datalog rules (and DLP with Datalog semantics) would effectively establish two Semantic Webs, with little or no semantic interoperability between the rules based Semantic Web and the ontology based Semantic Web, even at the RDF level. These two versions of the Semantic Web would inevitably be in competition with each other, and this would make the Semantic Web much less appealing: new users would be presented with a difficult choice as to which part to choose, and in choosing would sacrifice semantic interoperability with the other part."
3 comments:
DLP - Description Logic Programming. The way I see Datalog was an attempt to extend traditional databases to do some of the more nifty logical operations such as transitive closure. A quick Google gave me:
http://www.ruleml.org/papers/tutorial-ruleml-20050513.html
Most people are used to a Datalog approach as it's very similar to SQL databases.
There are some assumptions that are contradictory between Datalog and OWL. Datalog makes the "Closed World Assumption" and OWL makes the "Open World Assumption". The paper mentions things like counting and negation which can be done in Datalog and is not semantically compatible with OWL.
To me, closing and opening the world seems to make sense at certain times but I think most people are arguing for a consistent approach. They mention a logic framework to combine the two semantics which to me seems to make sense.
Your comment about queries being closed because distinguished variables (addressable concepts of an ontology, if you will) are only able to bind with named individuals is very interesting. I take it, by your comment, that you propose this: for queries within a given domain, which wish to remain open, there must be a sufficiently accomodating domain ontology that addresses at least the understanding of all potential concepts, entities, and relationships that might need to become part of a domain query.
In other words, the argument for a domain-wide (which is different from universal) upper ontology.
Am I right in seeing this in your proposed idea?
I was just quoting from the paper.
I guess that the point of developing ontologies is to provide a shared meaning between different systems. So the ontology must be broad enough to encompass broad usage. I do think a bottom up approach that develops through time is the best way to go about developing these ontologies.
I may have a fairly tainted view but a lot of the operations in refactoring code seem to have similarities to modifying ontologies.
I haven't done that much so it will be interesting to see if more experience sheds more light on this.
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