Specification and implementation of programs for updating incomplete information databases

The problem of updating incomplete information databases is examined as a programming problem. From this point of view formal denotational semantics are developed for two applicative programming languages, BLU and HLU. BLU is a very simple language with only five primitives, and is designed primarily as a tool for the implementation of higher level languages. The semantics of BLU are formally developed at two levels possible worlds and clausal and the latter is shown to be a correct implementation of the former. HLU is a user level update language. It is defined entirely in terms of BLU, and so immediately inherits its semantic definition from that language. This demonstrates a level of completeness for BLU as a level of primitives for update language implementation. The necessity of a particular BLU primitive, masking, suggests that there is a high degree of inherent complexity in updating logical databases.