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. 17. A computer according to claim 16 , wherein when a query is executed at a given time and specifies a timeslice earlier that precedes the given time, facts that match the query and that have lifespans that correspond to the timeslice are returned as satisfying the query, even though some of the returned facts have lifespans ending prior to the given time.