1. A method performed by one or more computers, the method comprising: executing a graph-store, the graph-store providing graph querying semantics to access facts stored in the graph-store, the graph-store including a first set of facts each of a first fact type; in response to a first user update submitted to the graph-store that comprises values of a new given fact of the first time, adding the given fact and its values to the graph-store, automatically adding time information to the stored given fact that indicates a time of adding the given fact to the graph-store; and in response to a second user update submitted to the graph-store that requests deletion of the given fact, automatically modifying the given fact in the graph-store to indicate that the given fact is no longer valid and to indicate a time of deleting the given fact.