Presents first-hand experiences from an actual re-engineering project. Business re-engineering is a process affecting not only the software system involved, but the underlying business model as well. Indeed, it is the changed business model along with the new technologies that determine the design of the new system. This paper is a walkthrough of the design of PICSDESK, a prototype incorporating some modern technologies to support the old business model of its predecessor and its evolution to a new business model. PICSDESK may be thought of as an example of a new breed of inventory control systems.

yatin~bellcore.com will scale up gracefully to more expressive data models and languages.

We investigate the complexity of various optimization techniques for logic databases. In particular, we provide polynomial-time algorithms for restricted versions of common program transformations, and show that a minor relaxation of these restrictions leads to NP-hardness. To this end, we define the k-containment problem on conjunctive queries, and show that while the 2-containment problem is in P, the 3-containment problem is NP-complete. These results provide a complete description of the complexity of conjunctive query containment. We also extend these results to provide a natural characterization of certain optimization problems in logic databases, such as the detection of sequencability and commutativity among pairs of Linear rules, the detection of 1-boundedness in sirups, and the detection of ZYT-linearizability in simple nonlinear recursions.

A number of optimizations have been proposed for Datalog programs involving a single intensional predicate (“single-IDB programs”). Examples include the detection of commutativity and separability ([Naug88],[RSUV89], [Ioan89a]) in linear logic programs, and the detection of ZYT-linearizability ([ZYT88], [RSUV89], [Sara89], [Sara90]) in nonlinear programs. We show that the natural generalizations of the commutativity and ZYT-linearizability problems (respectively, the sequencability and base-case linearizability problems) are undecidable. Our constructions involve the simulation of context-free grammars using single-IDB programs that have a bounded number of initialisation rules. The constructions may be used to show that containment (or equivalence) is undecidable for such programs, even if the programs are linear, or if each program contains a single recursive rule. These results tighten those of [Shmu87] and [Abit89].

The replacement of nonlinear recursions with equivalent linear recursions is a potentially useful query optimization strategy, since it permits the use of efficient algorithms for the evaluation of linear logic programs. We show that a member of a certain class of bilinear recursions is linearizable in a strong sense if and only if a specific partial proof tree derived from this recursion is contained in a bounded number of partial proof trees generated by the recursion. Further, while each such test of containment between proof trees involves an exponential number of conjunctive-query containment tests, we present syntactic conditions on the recursion that are necessary and sufficient for the containment and verifiable in polynomial time.