RDF store tables

The following tables contain metadata about the RDF store:

• One metadata table, which has the same name as the RDF store.
• The System Predicates metadata table, which stores information about RDF predicates that you can use for further filtering results of a SPARQL query.
• The Basic Statistics table, which stores statistics about the data in the RDF store.
• The Top K Statistics table, which stores information about the least selective RDF data in the store.

The following tables store RDF data if the value of the data does not exceed a particular character length:

• The Direct Primary table stores RDF triples and the associated graph, indexed by subject. Predicates and objects for a subject are stored in pair columns in this table. A particular predicate can occur in any one of three columns in this table. The object for that predicate is stored in the corresponding object column of the predicate-object pair.
• The Direct Secondary table stores RDF triples that share the subject and predicate within an RDF graph. Such triples have only a placeholder identifier in the Direct Primary table.
• The Reverse Primary table stores RDF triples and the associated graph, indexed by object. Predicates and subjects for an object are stored in pair columns in this table. A particular predicate can occur in any one of three columns in this table and the subject for that predicate can occur in the corresponding subject column of that pair.
• The Reverse Secondary table stores RDF triples that share the object and predicate within an RDF graph. Such triples have a placeholder identifier in the Reverse Primary table.
• The Datatypes table stores the mapping of internal integer values for SPARQL data types, user-defined data types, and language tags.

If the value of an RDF subject, predicate, object, or graph exceeds a particular character length, the previously mentioned five tables store a placeholder identifier only. The actual value is stored in the Long Strings table.