What is Schema Version

τXSchema is a framework for creating and validating temporal XML documents, while using a temporal schema that consists of three components: a conventional XML schema document annotated with a set of temporal logical and physical annotations. Each one of these components can evolve over time to reflect changes in the real world. In addition, schema versioning has been long advocated to be the most efficient way to keep track of both data and schema evolution. Hence, in this chapter the authors complete τXSchema, which is predisposed from the origin to support schema versioning, by defining the operations that are necessary to exploit such a feature and make schema versioning functionalities available to end users. Precisely, the authors' approach provides a complete and sound set of change primitives and a set of high-level change operations, for the maintenance of each component of a τXSchema schema, and defines their operational semantics. Furthermore, they propose a new technique for schema versioning in τXSchema, allowing a complete, integrated, and safe management of schema changes.