Re: Strawman DAML+OIL Query Language Proposal

From: Frank van Harmelen (
Date: 08/28/01

Richard Fikes wrote:
(as part of his Strawman DAML+OIL Query Language Proposal at [0]):

> 1) As mentioned in yesterday's telecon, we need to look at the query
> languages being designed for RDF and XML to see where we can be
> compatible.

The most important compatability issue will be with languages designed
to query RDF Schema, since that is the only language among XML/RDF/RDF-S
that carries any semantics that comes close to DAML+OIL. As you know,
DAML+OIL has been designed with partial understandability by RDF-S
agents in mind, so it would make sense for a DAML+OIL query language to
be an extension of a/the RDF-S query language.

Currently, there is only one proposal for a query language for RDF
Schema: RQL developed by people at ICS/Forth on Crete, Greece.  (see
e.g. the message [1] at rdf-logic in March). All the other query language
for RDF are not Schema-aware. They don't accomodate any of the intended
semantics of the ontology primitives in RDF Schema (Class, SubClass,
Property, SubProperty, etc), so they are next to useless for

There are currently two independent implementations of RQL, one by the
Greek, one by a Dutch company (who is participating in one of our
European projects).

The best introduction to RQL is probably at the site of the Dutch
implementation. Their implementation is called Sesame (at [2]). At [3]
you can find a "babysteps to RQL" document to get a quick impression of
the language. Also, you can play with RQL queries on existing
repositories in a web-based freely available implementation of RQL.

My genuine impression is that RQL is a good piece of work, done by
people from the database community who know their stuff. RQL has been
designed similar to OQL, which is itself an OO-variety of SQL. Since
DAML+OIL is an extension of RDF Schema, it would be very natural/nice to
base any DAML+OIL query language on RQL. This would give a nice
succession of inclusions of query languages, starting with SQL, ending
up with a query language for DAML+OIL via a query language for RDF
Schema (all by language inclusion).



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