Output Format

[venkateshzifo]

Hi,

How to set the output format using the java code. I am getting the output as RDF triples now. I would like to get the output as JSON-LD. I would like to do this from the code. Do we need to define it somewhere with executor object ? Could you please help me on this ?

[bjdmeest]

Hi,

The executor.execute-command returns a QuadStore, which has a write method that takes the format as one of the parameters. For example, the snippet below writes the output as jsonld to stdout.

QuadStore result = executor.execute(triplesMaps, checkOptionPresence(removeduplicatesOption, lineArgs, configFile), metadataGenerator);
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
result.write(out, "jsonld");

Does this help?

[venkateshzifo]

Thanks for the response.

Yeah that's what I am looking for. But its not working

It throws Serialization jsonld not supported when I try to write the output as jsonld.

[bjdmeest]

Ah, could it be that you are using a SimpleQuadStore instead of a RDF4JStore when creating the Executor?

Executor executor = new Executor(rmlStore, factory, functionLoader, outputStore, Utils.getBaseDirectiveTurtle(is));

The outputStore of this line should be an RDF4JStore.

[venkateshzifo]

I am using below code snippet. I am using RDF4JStore only.

                InputStream mappingStream = new FileInputStream(mappingFile);

		Model model = Rio.parse(mappingStream, "", RDFFormat.TURTLE);

		RDF4JStore outputStore = new RDF4JStore(model);

		Executor executor = new Executor(outputStore, new RecordsFactory(new DataFetcher(cwd, outputStore)));

		QuadStore chromResult = executor.execute(executor.getTriplesMaps());

		chromResult.removeDuplicates();

		BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
		
                chromResult.write(out, "jsonld");`

[bjdmeest]

Ah, yes, there's a bit of confusion here: you need QuadStore for your RML mapping, and a second QuadStore for your output data. You can check https://github.com/RMLio/rmlmapper-java/blob/master/src/main/java/be/ugent/rml/cli/Main.java for more details, but I guess you need something along the lines of

// Read mapping file
InputStream mappingStream = new FileInputStream(mappingFile);
Model model = Rio.parse(mappingStream, "", RDFFormat.TURTLE);
RDF4JStore rmlStore= new RDF4JStore(model);
// Load functions
FunctionLoader functionLoader = new FunctionLoader(null, null, new HashMap<>());
// Prepare output store
RDF4JStore outputStore = new RDF4JStore();
// Create executor
Executor executor = new Executor(rmlStore, new RecordsFactory(new DataFetcher(cwd, rmlStore)),functionLoader, outputStore, Utils.getBaseDirectiveTurtle(mappingStream ));
// Execute
QuadStore chromResult = executor.execute(executor.getTriplesMaps());
chromResult.removeDuplicates();
// Write result
BufferedWriter out = new BufferedWriter(new OutputStreamWriter(System.out));
chromResult.write(out, "jsonld");`

[venkateshzifo]

I am facing new problem with this code. Utils.getBaseDirectiveTurtle is not available method in Utils class. Is this from be.ugent.rml.Utils class ?

[bjdmeest]

Indeed, please see https://github.com/RMLio/rmlmapper-java/blob/master/src/main/java/be/ugent/rml/cli/Main.java for the imports

[venkateshzifo]

Thanks, It worked, the problem is, I was using older jar. Thanks for helping out :)