Providing Time-Related Constraints for Conventional Database Systems

A model for a historical database is described which is based upon time-stamped tuples as the unit of storage. The model includes both physical and logical time-stamps. The technical characteristics of write-once laser discs prevent the use of double logical time-stamps. The model distinguishes version from correction-updates. It is shown that if set-valued attributes are involved the use of null values is unavoidable if backdated correction-updates are allowed. A method of handling user-defined integrity constraint rules is outlined which involves the maintenance of a time-stamped trace of such rules. Such a trace is necessary for the proper handling of backdated correction-updates. An outline of a system SIS-BASE is described which implements some of these ideas.