Re: union graph

[Chris Jones]

On 8/22/2016 7:33 AM, Jean-Marc Vanel wrote:
Try a FILTER clause involving ?g1 and ?g2 .

I don't see how that would be any better; I'd still be specifying two 
separate graphs ?g1 and ?g2, instead of a union graph ?g. Is there 
something I don't understand?

there is also the unionGraph but it takes everything in all named graphs .

Thanks, but that's definitely not what I want. I want a way to take only 
some of the named graphs.

Is there a way to do a CONSTRUCT as a subquery, and perform my select 
against the results of that subquery?

Chris


2016-08-22 15:21 GMT+02:00 Chris Jones <ch...@cjones.org>:

Hi All,

Is it possible to run a query against the union of a bunch of named
graphs, where each named graph is selected by some logic? As an example, I
have something like this:

select ?attr ?value ?attrName where {
     graph ?g1 {
         ?subj ?attr ?value .
     }
     graph ?g2 {
         ?attr rdfs:label ?attrName .
     }
     ?g1 xyz:good true .
     ?g2 xyz:good true .
}

...so I'm grabbing data from g1, and metadata from g2. Both g1 and g2 are
selected using some kind of logic; and they might be the same graph. You
can imagine a larger query, expressed in this style, could get very
complex. Is there instead a way to specify a union graph made up of all the
graphs for which a predicate is true, and then perform a query against that
union graph?

Chris