[Mulgara-general] Reification in Mulgara (with example this time)

[Paul Gearon]

On Tue, Oct 27, 2009 at 3:58 PM, Alex Black <alex at alexblack.ca> wrote:
> Is reification supported in Mulgara/TQL?

Like most triple stores, you have to reify manually. It's not a
particularly common thing to do these days. Do you have a particular
need for it?

> I'm trying to execute these queries using the tutorial web interface:
>
> a. Insert a triple
>
> insert <foo> <bar> <me> into <rmi://alex-pc1/server1#sampledata>
>
> b. Try to find that triple
>
> select
> ?st from <rmi://alex-pc1/server1#sampledata>
> where
> ?st <http://www.w3.org/1999/02/22-rdf-syntax-ns#subject> <foo>
> and
> ?st <http://www.w3.org/1999/02/22-rdf-syntax-ns#predicate> <bar>
> and
> ?st <http://www.w3.org/1999/02/22-rdf-syntax-ns#object> <me>;
>
> I get:
>
> HTTP ERROR: 400
>
> Error executing command. Reason: java.lang.NullPointerException
>
> RequestURI=/tutorial/ExecuteQuery.html

Errrr, *that* shouldn't happen. You should just get an empty result
(because you didn't reify the statement). I'll check into why that
error appeared.

Even if we did support reification, it wouldn't happen like this. You
don't want everything in your system reified. There are all sort of
nasty implications with that. It's also possible to reify a statement
that doesn't exist.

Paul