The W3C XML Schema recommendation defines the structure and data types for XML documents. An XML document evolves as it is updated over time or as it accumulates from a streaming data source. A temporal document records the entire history of a document rather than just its current state or snapshot. Capturing a document's evolution is vital to providing the ability to recover past versions, track changes over time, and evaluate temporal queries. XML Schema lacks explicit support for time-varying XML documents. Users have to resort to ad hoc, non-standard mechanisms to create schemas for time-varying XML documents.

In this thesis we introduce TXSchema, which is an extension of XML Schema, infrastructure, and a suite of tools to support the creation and validation of time-varying documents, without requiring any changes to XML Schema. The data model and architecture support the creation of a temporal schema from a non-temporal (snapshot) schema, a temporal annotation, and a physical annotation. These annotations specify, respectively, which portion(s) of an XML document can vary over time, how the document can change, and where timestamps should be placed. The advantage of using annotations to denote the time-varying aspects is that logical and physical data independence for temporal schemas can be achieved while remaining fully compatible with both existing XML Schema documents and the XML Schema recommendation. A Temporal Validator augments a conventional validator to more comprehensively check the validity constraints of a document, especially temporal constraints that cannot be checked by a conventional XML Schema validator.

We then extend TXSchema to support versioning of the schema itself. When the schema is versioned, the base schema and the temporal and physical annotations can themselves be time-varying documents, each with their own (possibly versioned) schemas. We describe how a temporal data validator can be extended to validate documents in this seeming precarious situation of data that changes over time, while its schema and even its representation are also changing.

Advisor : Dr.Richard Snodgrass
Co-Advisor: Dr.Curtis Dyreson