Balisage Paper: Identity constraints for XML
Anne Brüggemann-Klein
Technische Universität München
Mustapha Maalej
Technische Universität München
Marouane Sayih
Technische Universität München
Copyright © 2014 by the authors. Used with permission.
Abstract
Identity constraints, a fundamental database concept, are built in to XML Schema. In this paper, we attempt to explain clearly our reading of XML Schema's identify constraint concepts. We illustrate our reading with examples, in the style of a tutorial. We also illustrate usage styles and limitations of identity constraints in XML Schema. Finally, we demonstrate how a more general notion of identity constrains that is adapted to the hierarchical nature of XML documents can be expressed with XPath 2.0. Hence, the limitations that we have identified can be by-passed with assertions as introduced by XML Schema 1.1.