Abstract

Views are a central component of both traditional database systems and new applications such as data warehouses. Very often the desired views (e.g. the transitive closure) cannot be defined in the standard language of the underlying database system. Fortu-nately, it is often possible to incrementally maintain these views using the standard language. For exam-ple, transitive closure of acyclic graphs, and of undi-rected graphs, can be maintained in relational cal-culus after both single edge insertions and deletions. Many such results have been published in the theoret-ical database community. The purpose of this survey is to make these useful results known to the wider database research and development community. There are many interesting issues involved in the maintenance of recursive views. A maintenance al-gorithm may be applicable to just one view, or to a class of views specified by a view definition language such as Datalog. The maintenance algorithm can be specified in a maintenance language of different ex-pressiveness, such as the conjunctive queries, the re-lational calculus or SQL. Ideally, this maintenance language should be less expensive than the view def-inition language. The maintenance algorithm may allow updates of different kinds, such as just single tu-ple insertions, just single tuple deletions, special set-based insertions and/or deletions, or combinations thereof. The view maintenance algorithms may also need to maintain auxiliary relations to help maintain the views of interest. It is of interest to know the minimal arity necessary for these auxiliary relations

Citations