Efficient View Self-Maintenance, A TECHNICAL REPORT

Abstract

We revisit the problem of finding a maximal test that guarantees that a view can be maintained using only the view, its definition and the update, regardless of the actual database instance. These maximal tests, we call Complete Tests for View Self-Maintainability (abbrev are also known in the literature as necessary and suffcient conditions for Conditionally Autonomously Computable Updates ([TB88This paper focuses on finding an effcient evaluation of self-maintainability (abbrev Our working hypothesis is that at least for conjunctive-query (abbrev CQ) views (i.e. select-project-join views with only equality SM evaluation can be separated into a view-definition-time portion where a maximal test is generated solely based on the view definition, and an update-time portion where the test is actually applied to the view and the update. We also conjecture that these tests can be expressed as queries over the view in some traditional query language. The obvious practical significance would be that CTSM's not only can be precomputed but can also be optimized using traditional query optimizers, thus minimizing work that needs to be done at update time. Unlike previous work, we use an alternative formulation of SM and a different approach for deriving CTSM. This paper reports on some interesting new results for insertion updates and CQ views: 1) the CTSM's are extremely simple queries that look for certain tuples in the view to be maintained; 2) these CTSM's can be generated at view definition time using a very simple algorithm based on the concept of Minimal Z-Partition; 3) view self-maintenance can also be expressed as simple update queries over the view itself.