Help on FROM keyword

[Andrea Gazzarini]

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