Database query languages embedded in the typed lambda calculus

Abstract

It is shown how to naturally embed, in the typed lambda -calculus with equality, many database query languages, including the relational calculus/algebra, inflationary Datalog, and the complex object calculus/algebra. The embeddings considered are such that a database is a lambda -term coding list of tuples and a query is a lambda -term which when applied to the input database normalizes to the output database. In addition, if the query expressed is a PTIME query, then the normal form can be computed in a number of reduction steps polynomial in the size of the input database. It is also shown that, for all PTIME queries, there is such an embedding in the order-three typed lambda -calculus with equality.<>