Add the ability to save RDF models

[agarciadom]

At the moment, the driver can only read RDF documents. At some point we need to add the ability to create new RDF resources, link them together, add properties, and save back the result.

This would probably have to wait until we have thought out the MOF2RDF mapping.

[OwenR-York]

Example of writing model to file in Turtle

        private Model model;  // should work with OntModel Class too.
	public void outputTTLFile() throws Exception {
		FileWriter file = new FileWriter("./resources/OWL/Model.ttl");
		model.write(file, "TTL");
		file.close();
	}

[OwenR-York]

The preferred method for saving models is to use Output Streams, the writer can have character encoding issues.

Also, there is a .writeALL method which writes all imported and inferred triples.

	public void outputTTLFile() throws Exception {
		String path = "./resources/temp/savedModel.ttl";
		System.out.println("Saving to file: " + path);
		FileOutputStream file = new FileOutputStream(path);
		model.saveOntModel(file, "TTL");
		file.close();
	}

[OwenR-York]

When saving/editing models there is a need for caution with the type of Class being used to handle the model.

A user's data model can be handled using Model or OntModel. When a user's data model is unchanged when handled using a Model. However, an OntModel adds additional information (triples) to the model (presumably to support Jena's Ont API).

Similarly, if a user's data model is passed to a reasoner with a schema; the resulting inferred model will contain triples not in the original data model (and likely not wanted) and should not be written out or edited.

[agarciadom]

Thanks for looking into this! In the future, we may want to have separate RDFModel and OntRDFModel classes, and note in the documentation that saving OntRDFModels will have this issue about extra tuples being saved. (People may actually want this behaviour sometimes, just to see all the extra information that was inferred.)

A reminder: when doing I/O, please use try-with-resources blocks so that we always close the file properly.