13. One or more computer-readable storage media according to claim 12 , wherein when a fact is logically deleted it is automatically removed from the first table and automatically added to the second table and a corresponding valid-to time value is added to the logically deleted fact, the logically deleted fact including a same valid-from time value that it had when it was stored in the first table.
12. One or more computer-readable storage media according to claim 8 , wherein the semantic data store stores currently valid facts in a first table and stores currently invalid facts with valid-to time values in a second table.