Re: Help on FROM keyword

[Andy Seaborne]

On 13/05/15 20:16, Andrea Gazzarini wrote:
Hi Andy,
Thank you very much for the explanation. But I still miss the point: as you
said, the FROM keyword set / fills the default graph so assuming I
previously loaded a triple under http://graph1.com
Running

SELECT ?s FROM <http://graph1.com> { ?s ?p ?o }

I should get the subject of that triple. Is that correct? Because the code
above is running under this exact scenario and I'm getting no result.

It will do an HTTP GET on http://graph1.com -- it does not get it from 
the dataset because its the dataset to be queried that is being described.

(graph1.com happens to exist and it returns junk.)

        Andy


Kind Regards,
Andrea
On 13 May 2015 21:05, "Andy Seaborne" <a...@apache.org> wrote:

FROM describes the dataset to use.

GRAPH accesses the data.

FROM <http://example/data> set the default graph from the contents of
http://example/data by reading that URL. (This is for the general purpose
dataset - TDB is slightly different but the principle is the same)

         Andy

On 13/05/15 18:57, Andrea Gazzarini wrote:

Hi Trevor,
Thanks, yes that works...but I would like to understand what is wrong with
my example

Thanks again
Andrea
On 13 May 2015 19:54, "Trevor Donaldson" <tmdona...@gmail.com> wrote:

  Hi Andrea,

Can I suggest trying this ..

SELECT ?s
WHERE {
    GRAPH <http://graph1.com> {
    ?s ?p ?o
   }
}

On Wed, May 13, 2015 at 1:26 PM, Andrea Gazzarini <gxs...@gmail.com>
wrote:

  Hi,
A question about the FROM keyword. I have the following data

<http://graph1.com> = { <http://a.b.c/s1> <http://a.b.c/p1> <
http://a.b.c/o1>
. }
<http://graph2.com> = { <http://a.b.c/s2> <http://a.b.c/p2> <
http://a.b.c/o2>
. }

For simplicity, I created a file for each triple (file1.nt and
file2.nt).
Then, I loaded those data using the following code:

Dataset memoryDataset = DatasetFactory.createMem();
Model memoryModel = ModelFactory.createDefaultModel();
memoryModel.read(new FileReader("file1.nt"), "http://e.org";,

"N-TRIPLE");

memoryDataset.addNamedModel("http://graph1.com";, memoryModel);

memoryModel = ModelFactory.createDefaultModel();
memoryModel.read(new FileReader("file2.nt"), "http://e.org";,

"N-TRIPLE");

memoryDataset.addNamedModel("http://graph2.com";, memoryModel);

I'm not understanding the results coming from the following query:

SELECT ?s FROM <http://graph1.com> { ?s ?p ?o }

?s = <nothing>

I was expecting

?s=<http://a.b.c/s1>

Am I missing something? I'm using Jena 2.12.1

Thanks in advance for your help
Andrea