9 - Validation beyond XML Schema

Abstract

This chapter discusses structural document validation. XML schema allows one to define constraints that refer to the content of elements of attributes in the form of simple data types. This chapter discusses various methods for modeling and implementing advanced semantic constraints such as cross-field and cross-document constraints. The classical method is to hardcode constraints using imperative programming with programming languages such as Java, C++, or Perl. Alternatively, it is possible to softcode constraints as rules in the form of XSLT stylesheets or as Schematron schemata. In all these methods, XPath plays a pivotal role as a common language to formulate constraints. With this abundance of schema languages and validation methods, this chapter analyzes the individual steps during the validation of a document and how the various schema languages cover them. This chapter concludes with a discussion on a current standardization effort for the integration of these diverse approaches to schema validation.