metaGraphId = (String) (configuration.get(OntologyProvider.META_GRAPH_ID));
if (metaGraphId == null) metaGraphId = _META_GRAPH_ID_DEFAULT; // Should be already assigned though
// This call will also create the metadata graph.
keymap = new OntologyToTcMapper();
descriptor = new MGraphMultiplexer(keymap.graph);
// Parse configuration.
prefix = (String) (configuration.get(OntologyProvider.GRAPH_PREFIX));
if (prefix == null) prefix = _GRAPH_PREFIX_DEFAULT; // Should be already assigned though