Independently updated views

Abstract

Independently updated views (IUVs) are updated versions of a relational view. Unlike traditional views, updating an IUV changes only that IUV and not the underlying database. Updates to an IUV are stored in a differential table (DT) and incorporated when the IUV is accessed. There is no restriction on the type of query used to define the IUV. Applications of IUVs include alternative scenarios for decision support, local updating of distributed snapshots, and CAD versioning. IUVs allow versions to be defined on dynamic databases. This may cause inconsistencies because both the IUV and the base tables on which the IUV is defined can be updated independently of one another. We introduce "overlapping updates" that cause such inconsistencies and present algorithms for their detection and resolution using timestamps. These algorithms do not impose additional overhead on the database and require only the modification of the DT. A performance analysis indicates that the cost of querying IUVs is reasonable for a wide range of queries, views, and access strategies. We also consider a materialized implementation of IUVs. Materialized IUVs do not require a DT, relying instead on additional system columns for operation codes and timestamps. Results suggest a mix of implementation strategies for different types of IUV applications, depending on the frequency and nature of queries on the IUVs, the IUV sizes, and how actively the base tables are updated.