Merge RDF .ttl files into one file database - filtering and keeping only the data/triples needed

Question

I need to merge 1000+ .ttl files into one file database. How can I merge them with filtering the data in the source files and keep only the data needed in the target file?

Thanks

Answer 1

There's a number of options, but the simplest way is probably to have use a Turtle parser to read all the files, and let that parser pass its output to a handler which does the filtering before in turn passing the data to a Turtle writer.

Something like this would probably work (using RDF4J):

  RDFWriter writer = org.eclipse.rdf4j.rio.Rio.createWriter(RDFFormat.TURTLE, outFile);

  writer.startRDF();
  for (File file : // loop over your 100+ input files) {
      Model data = Rio.parse(new FileInputStream(file), "", RDFFormat.TURTLE);
      for (Statement st: data) {
         if (// you want to keep this statement) {
              writer.handleStatement(st);
         }
      }
  }
  writer.endRDF(); 

Alternatively, just load all the files into an RDF Repository, and use SPARQL queries to get the data out and save to an output file, or if you prefer: use SPARQL updates to remove the data you don't want before exporting the entire repository to a file.

Something along these lines (again using RDF4J):

 Repository rep = ... // your RDF repository, e.g. an in-memory store or native RDF database

 try (RepositoryConnection conn = rep.getConnection()) {

    // load all files into the database
    for (File file: // loop over input files) {
        conn.add(file, "", RDFFormat.TURTLE);
    }

    // do a sparql update to remove all instances of ex:Foo
    conn.prepareUpdate("DELETE WHERE { ?s a ex:Foo; ?p ?o }").execute();

    // export to file
    con.export(Rio.createWriter(RDFFormat.TURTLE, outFile));
 } finally {
    rep.shutDown(); 
 } 

Depending on the amount of data / the size of your files, you may need to extend this basic setup a bit (for example by using transactions instead of just letting the connection auto-commit). But you get the general idea, hopefully.