XCSL tutorial

Abstract

XML brought the concept of well-formmedness to the world of structured documents. An XML document can be well-formed or valid. To be valid it just has to convey certain rules specified in a DTD or XML Schema. DTDs enable us to specify structure rules and a little bit of dynamic semantics. Additionally, XML Schemas enable us to specify some static semantics. However, there are applications where we need to specify more complex invariants or constraints. Some of these constraints are structural but many of them are non-structural and have some degree of complexity. Here is where XCSL comes into scene, enabling to specify this extra semantics. This tutorial presents an XML based architecture that enables the specification of constraints, the kind of constraints we can not specify with DTDs. XCSL is not just a language, it is also a processing model. We also discuss the general philosophy underlying the proposed approach, presenting the architecture of our semantic validation system, and we detail the respective processor. To illustrate the use of the XCSL language and the subsequent processing, we present a complete case-study showing, step-by-step, the way we handled the various problems it raises. By making the analysis of this casestudy and following the explanation, it should be easy to use XCSL with every family of documents one comes across.