RDF support is a core feature of Fedora 4, used as the primary data format for the REST API. A triplestore is not bundled into the repository itself. Instead, Fedora 4 sends events when the repository is updated, and the Indexer copies RDF from the repository to an external triplestore to keep it in sync with the repository. This pattern, which is also used for search functionality for the same reasons, allows maximum flexibility about what triplestore to use, and removes the overhead of keeping the triplestore in sync from the core repository functionality.
In order for resources to be indexed in the triplestore, they must be flagged as "indexable". See documentation under External Search for how to mark resources for indexing.
