Abstract State Machines and Computationally Complete Query Languages

Abstract

Abstract state machines (ASMs) form a relatively new computation model holding the promise that they can simulate any computational system in lockstep. In particular, an instance of the ASM model has recently been introduced for computing queries to relational databases. This model, to which we refer as the BGS model, provides a powerful query language in which all computable queries can be expressed. In this paper, we show that when one is only interested in polynomial-time computations, BGS is strictly more powerful than both QL and ${{\it while}_{\it new}}$, two well-known computationally complete query languages. We then show that when a language such as ${{\it while}_{\it new}}$ is extended with a duplicate elimination mechanism, polynomial-time simulations between the language and BGS become possible.