Re: DQL Query Patterns and Variable Bindings

From: Richard Fikes (
Date: 12/13/01

In this message, I am going to reply only to your comments about the
part of my message that was stating the portion of DQL that I thought we
had agreed on.

> >Here is what I think we agreed on in last week's telecon:
> >
> >A query contains a query pattern that specifies a conjunction
> Do we want to allow conjunctions in the first instance? I would 
> suggest not, ie say 'a DAML+OIL expression'.

Most nontrivial queries will involve more than one
property-subject-object triple (e.g., (Owns ?p ?c) (Type ?c Red-Car))
and is therefore a conjunction of DAML+OIL sentences.  So, I think it is
important that the pattern specify a conjunction of DAML+OIL sentences. 
(And that is what we have all been saying to each other in our

> >of
> >DAML+OIL sentences in which /some/ literals and/or resource /name/s 
> >have been replaced
> >by variables.  A query includes a specification of which of the
> >variables in the query pattern are distinguished variables.  A query
> >answer includes a binding for each distinguished variable such that the
> >query knowledge base entails the sentence produced by replacing each
> >distinguished variable  in the query pattern by its binding and
> >considering the remaining variables in the query pattern to be
> >existentially quantified.
> There may also be restrictions on the ways that variables can occur 
> in the query pattern, eg requirements of no 'looping'. (We should 
> keep this possibility open, maybe?. )

Yes, as per our telecon discussion, I don't think such restrictions are
a good idea, but I will not stand in the way of there being such
restrictions in the language.  The floor is open for precise proposals
for such restrictions.

> >A binding for a distinguished variable can be one of the following:
> >
> >* A literal;
> >
> >* The name of a resource
> Does that mean a URI? If so, best to say that explicitly. (If not, 
> what other kind of resource names are contemplated?)

Yes, I meant a URI, and I agree that should be said explicitly.  So,
replace "The name of a resource" by "a URI".

> >* A "blank" name that corresponds to an anonymous resource that occurs
> >in the query kb.
> rephrase:
> *A "blank" name that indicates that a binding has been found, but its 
> scope is local to the KB.

Well, I was trying to be more precise than that.  I think we mean for
"blanks" to refer to anonymous nodes, as per your RDF Model Theoretic
Semantics.  We probably don't won't to spend time on this issue until
the relationships between RDF and DAML+OIL are sorted out.


This archive was generated by hypermail 2.1.4 : 04/02/02 EST