The expressiveness of DAC

We de.ne a new logic-based query language, called DAC, which is an extension of Datalog. A DAC(w(n); h(n))(b(n))-program consists of a family of Datalog programs Pn such that w(n); h(n); b(n) bound the width of rules, the number of rules, and the recursion depth of any Pn, respectively. We exhibit queries which are not Datalog expressible but are DAC expressible. We also prove non-expressiveness results for DAC and we infer various strict hierarchies obtained by allowing more rapidly growing functions on the bound parameters. c © 2002 Elsevier Science B.V. All rights reserved.