What is Schema Versioning

In information systems, not only do data change over time, but also database schemata evolve frequently as a response to evolving application requirements. In the literature, schema evolution and schema versioning are the two techniques that were proposed to support schema changes in a DBMS, without loss of extant data and with continued support of legacy applications. After applying schema changes, schema evolution keeps only the current schema version and retains the data which are adapted to such a schema. On the other hand, each time schema changes are applied, schema versioning creates a new schema version, while preserving old schema versions and their corresponding data. With schema versioning, data access through any schema version is supported, which avoids applications developed with past schemata to become obsolete. The main goal of this chapter is to present the recent research proposals that deal with schema versioning and to discuss the recent advances on schema versioning support in mainstream DBMSs.