The large dynamicity of XML documents on the Web has created the need to adequately support structural changes and to account for the possibility of evolving and versioning the schemas describing XML document structures. This chapter discusses and compares the support for schema evolution and versioning provided by commercial systems as well as the most relevant approaches and prototypes proposed and developed by the research community.
In this section, we first introduce some basic notions about XML documents and schemas and briefly present the languages for manipulating XML documents. Then, we discuss the role of schemas in XML data management systems. Finally, the concepts of schema modification, evolution, and versioning are introduced and contrasted.