16. A computer comprising storage and a processor, the storage storing: a graph store storing a graph of facts, the facts conforming to a schema describing the graph, wherein each fact comprises a triplet comprising a subject value, a predicate value, and an object value, wherein the facts are instances of varying different fact types that have different subject data types and/or different predicate data types and/or different object data types, and wherein the semantic graph store is configured to receive semantic queries for facts in the graph store, wherein when facts are stored by automatically maintaining information indicating lifespans of each fact in the graph store.
16. A computer comprising storage and a processor, the storage storing: a graph store storing a graph of facts, the facts conforming to a schema describing the graph, wherein each fact comprises a triplet comprising a subject value, a predicate value, and an object value, wherein the facts are instances of varying different fact types that have different subject data types and/or different predicate data types and/or different object data types, and wherein the semantic graph store is configured to receive semantic queries for facts in the graph store, wherein when facts are stored by automatically maintaining information indicating lifespans of each fact in the graph store. 20. A computer according to claim 16 , wherein the graph store receives graph queries having graph semantics and form, and converts the queries into relational database queries to be executed against a relational database storing the facts.