Using API Classes Instead of RDFhelper

This section contains a short guide on how to use the API classes of RDFHelper.

Read data to get a list of graphs within the data unit.

Further, lets start by showing how as a DPU developer you may iterate over the input data unit in order to get access to RDF graphs which comes over input RDF data unit. The code below goes to innerExecute() method of the DPU.

Code 1 - Iterating over input RDF graphs using API classes

Set<URI> rdfGraphs = new HashSet<>();
FilesDataUnit.Iteration it = null;
try {
    it = input.getIteration();
    while (it.hasNext()) {
        final URI dataGraphURI = it.next().getDataGraphURI();
        rdfGraphs.add(dataGraphURI);
    }
} catch (DataUnitException ex) {
    throw ContextUtils.dpuException(ctx, ex, "dpuName.error");
} finally {
    if (it != null) {
        try {
            it.close();
        } catch (DataUnitException ex) {
            log.error("Error on close.", ex);
        }
    }
}
 

So after executing Code 1, we have a set of RDF graphs in which the input RDF data (triples) reside in the variable rdfGraphs. We may then work with the RDF graphs using standard approach of OpenRDF API.

The code introduced in Code1 can be simplified by using helper - eu.unifiedviews.helpers.dataunit.rdf.RDFHelper in uv-dataunit-helpers. See Working with the RDF Data Unit. In this case, DPU developer does not need to manually handle iteration over input RDF graphs.

In general, as a DPU developer you should use helpers, if possible.

There are two methods as DPU developers you may use to add graphs to output RDF data unit:

In order to add existing RDF graph to the output data unit, the code below may be used in the innerExecute() method of the DPU.

Code 4 - Creating RDF graph in the output data unit using API classes

String graphName = ...
URI graphURI = ...
Symbolic symbolicName = output.addExistingDataGraph(graphName, graphURI);