Query processing in PIOS

An approach to query processing in object-oriented stores supporting physical data independence is proposed in this Chapter. In particular, the problem of query optimisation (i e finding efficient execution plans for declarative queries) is investigated. A set of rewrite rules has been defined in order to allow an algebraic optimisation phase. A local search procedure, based on a cost model of the store, has been tailored to the task of physical optimisation. To support the physical data independence in the store, a translation algorithm, dealing with the actual storage organisation of the database, has been studied. A comprehensive example illustrates these mechanisms. Finally, performance results are presented.