Re: dataset assembler for JENA-624

[Andy Seaborne]

On 05/11/15 16:49, Andy Seaborne wrote:
On 05/11/15 16:11, A. Soroka wrote:
On Nov 5, 2015, at 11:02 AM, Andy Seaborne <a...@apache.org> wrote:
On 05/11/15 15:44, A. Soroka wrote:
Yeah, I basically copied the “parallel semantics” of ja:graph and
ja:defaultGraph from DatasetAssembler. Perhaps I misunderstood them?
If you think it's a problem, do you have a better name?

I’m now a bit confused about what they mean and what ja:data is
supposed to mean, and I don’t want to spread my confusion any further!
{grin} To (try to) get some clarity: are they supposed to have the
same meaning (they do now in my PR, and I really think they do in
DatasetAssembler)? If they are supposed to have a different meaning,
and one of those meanings is “load from this URI”, what is the
difference in that and the newly-introduced ja:data predicate?


They are different.

If you call assembler.open for the object of ja:defaultGraph it will
create a model. It does not know about datasets at that point.  You get
a regular model in-memory.

Adding to the in-mem dataset with addNamedModel or setDefaultModel will
be a copy into the datastructures of the in-mem dataset.

The use cases for direct file loading are:


1/ Load file into dataset.
RDFDataMgr.read(dataset, file)
   Case 1a: quads
   Case 1b: triples


2/ Load file to graph
   Case 2a: default graph
        RDFDataMgr.read(dataset.getdefaultModel(), file)
   Case 2b: named graph
        RDFDataMgr.read(dataset.getNamedModel(), file)

Note: When asked to read triples and it's a quads file, the RDFDataMgr
outputs just the triples from the default graph of the input (it does
not know it's reading into a named graph - it's just a destination of a
stream of triples).

     Andy




In code, that is something like this: (error checking could be enhanced):

@Override
public Dataset open(final Assembler assembler, final Resource root, 
final Mode mode) {
    checkType(root, MemoryDataset);
    Dataset dataset = createTxnMem();
    setContext(root, dataset.getContext());

    // Case 1
    multiValue(root, pGraph).stream().map(RDFNode::asResource)
      .forEach(r->readGraphDesc(dataset, r));

    // Case 2
    multiValue(root, data).stream().map(RDFNode::asResource)
      .forEach(x -> RDFDataMgr.read(dataset, x.getURI()));

    // If desired:
    // ... ja:defaultGraph
    // ... ja:namedGraph

    return dataset;
}

(and I hope my plague of tabs got sorted out).

        Andy