From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 09/25/01
From: Richard Fikes <fikes@ksl.stanford.edu> Subject: DAML+OIL Query Language and RQL Date: Mon, 24 Sep 2001 11:05:55 -0700 > The text at the beginning of my initial message on DQL 0.1 was intended > to be an informal description of the language. I don't think I can do > much better than that and so will include it again here: > > ----------------------------------- > > An instance of class Query represents a question posed to a reasoner. A > query instance consists of two parts: a query premise and a query > pattern. A query premise is a DAML+OIL KB that is effectively asserted > to the queried KB for the duration of the query. It is to contain > assumptions particular to the current query. The query premise can be > empty to indicate the absence of such assumptions. A query pattern is > the question itself. It is in effect a conjunction of one or more > triples. Each triple corresponds to an RDF Statement except that its > predicate, subject, and/or object can be a variable. Variables present > in a query pattern, if any, are implicitly quantified existentially at > the beginning of the pattern. Syntactically, a query pattern is in xml > markup. > > An answer to a query specifies an instance of the query pattern all of > those RDF statements are entailed by the KB being queried conjoined with > the query premise KB. An instance of class QueryAnswer represents one > answer to a query. A query answer instance consists of two principle > parts: the query posed and a set of bindings to the query variables > representing an instantiation of those query variables. I would like to see a more-formal description of DQL in the near future. In particular, I would like to see a formal definition of what an answer is. (For example, what if there are two resources that are defined as being the same. Do these constitute one answer or two?) peter
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