Declarative updates of relational databases

This article presents a declarative language, called update calculus , of relational database updates. A formula in update calculus involves conditions for the current database, as well as assertions about a new database. Logical connectives and quantifiers become constructors of complex updates, offering flexible specifications of database transformations. Update calculus can express all nondeterministic database transformations that are polynomial time. For set-at-a-time evaluation of updates, we present a corresponding update algebra . Existing techniques of query processing can be incorporated into update evaluation. We show that updates in update calculus can be translated into expressions in update algebra and vice versa.