Reasoning Formally About Database Queries and Updates

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This paper explores formal verification in the area of database technology, in particular how to reason about queries and updates in a database system. The formalism is sufficiently general to be applicable to relational and graph databases. We first define a domain-specific language consisting of nested query and update primitives, and give its operational semantics. Queries are in full first-order logic. The problem we try to solve is whether a database satisfying a given pre-condition will satisfy a given post-condition after execution of a given sequence of queries and updates. We propose a weakest-precondition calculus and prove its correctness. We finally examine a restriction of our framework that produces formulas in the guarded fragment of predicate logic and thus leads to a decidable proof problem.