Seminario
(nell'ambito della lezione del corso di Sistemi informativi, aperto a tutti gli interessati)

Mercoledì 14 gennaio 2004, ore 14 aula N3

Dr. Themis Palpanas
University of California, Riverside (USA)

Abstract

Incremental view maintenance is a well-known topic that has been addressed in the literature as well as implemented in database products. Yet, incremental refresh has been studied in depth only for a subset of the aggregate functions. In this paper we propose a general incremental maintenance mechanism that applies to all aggregate functions, including those that are not distributive over all operations. This class of functions is of great interest, and includes MIN/MAX, STDDEV, correlation, regression, XML constructor, and user defined functions. We optimize the maintenance of such views in two ways. First, by only recomputing the set of \emph{affected} groups. Second, we extend the incremental infrastructure with work areas to support the maintenance of functions that are algebraic. We further optimize computation when multiple dissimilar aggregate functions are computed in the same view, and for special cases such as the maintenance of MIN/MAX, which are incrementally maintainable over insertions. We also address the important problem of incremental maintenance of views containing super-aggregates, including materialized OLAP cubes. We have implemented our algorithm on a prototype version of IBM DB2 UDB, and an experimental evaluation proves the validity of our approach.