RE: FW: [Jena-devel] FYI: New CVS module: BRQL

From: Butler, Mark <mark-h.butler_at_hp.com>
Date: Thu, 29 Jul 2004 16:22:29 +0100

Hi David

> Yes, that is what I understood from your previous post.
> But it seems that the "OPTIONAL" keyword is basically syntactic
> sugar for the kind of query I included in my email---where we use
> an existential over the property name and require it be one
> of the properties we care about.

> The syntactic sugar is certainly nice, but does the approach
> I mentioned work in plain RDQL?

I don't think it's just syntatic sugar. RDQL will let you use existentials
for all properties, but it doesn't support OR so you can restrict the
properties of interest. So for example in RDQL you can do this

SELECT *
WHERE (?a , rdf:type , vra:Image ) ,
         (?a , vra:subject, vraTopic:Architecture_artist) ,
       (?a, ?b, ?c)

which will give you all the properties of A (this is how RDQLHybrid model
works in Longwell). The problem with this is it will potentially return a
much bigger results set than if we specify the properties are interested in
using OPTIONAL, which is potentially a problem if running over HTTP.

Mark
Received on Thu Jul 29 2004 - 15:22:44 EDT