Schema Versioning

Since change is a fundamental aspect of persistent information and data-centric systems, both data and schema tend to change over time for a multitude of reasons, including to reflect a change in the real world, a change in the user’s requirements, mistakes in the initial design or to allow the expansion of the application scope over time. Schema versioning is a technique aimed at creating a new schema version while preserving old schema versions and their corresponding data after a schema change. Schema versioning has been investigated widely, both in the context of static and temporal databases. While schema changes are inevitable during the life of a database, current database management systems (DBMS) unfortunately do not provide support for schema versioning. With the growing interest in XML and XML data as well as the mechanisms for holding such data, some research work has recently been done also on the problem of schema versioning in XML databases. The purpose of this chapter is to present the different research proposals that deal with schema versioning.