Using witness generators to support bi-directional update between object-based databases (extended abstract)

‘I’his paper considers the issue of incrementally maintaining materialized replicated information in the context of objectbased databases. Uni-directional update concerns propagating updates in one direction, and is closely related to the materialized view update problem. Bi-directional update arises when two databases hold overlapping information, and users of either database have the authority to make updates to that information. The focus here is on the impact of object identifiers (OIDS). A restricted form of ILOG is used, that corresponds essentially to select-project-join queries extended to include OID invention. If auxiliary information is not maintained, then the uniand hi-directional update problems are shown to be essentially equivalent to the graph isomorphism problem, and thus probably intractable. A form of auxiliary information, called “witnesses”, can be used to bring the uni-directional update problem into LOGSPACE. For the hi-directional case a subtlety arises in connection with incremental maintanence of the witnesses. This paper presents a non-trivial procedure that can be used in a limited context for creating programs that maintain witnesses. If such “witness generator” programs are available, then the hi-directional update problem is also in LOCL5PACE.