Chapter 10: Case Study: XMLspec

Overview

This is the first of a group of three chapters that aim to show how all the facilities of the XSLT language can work together to solve real XML processing problems of significant complexity. I chose three example applications, with complete stylesheets for handling them. Most of the code is presented in these chapters, but the complete stylesheets, and specimen data files, can be downloaded from the Wrox Web site at http://www.wrox.com/ .

As I described in the previous chapter, XSLT has a broad range of applications, and in these three chapters I have tried to cover a representative selection of problems. The three examples I have chosen are as follows :

• The first example is a stylesheet for rendering sequential documents: specifically , the stylesheet used for rendering W3C specifications such as the XML and XSLT Recommendations. This is a classic example of the rule-based design pattern described on page 620 in Chapter 9.

• The second example, in Chapter 11, is concerned with presenting structured data. I chose a complex data structure with many cross-references to illustrate how a navigational stylesheet can find its way around the source tree: the chosen example is a data file containing the family tree of the Kennedys. This example is particularly suitable for demonstrating how stylesheets and schemas can work together.

• The final example stylesheet, in Chapter 12, is quite unrealistic , but fun. It shows how XSLT can be used to calculate a knight's tour of the chessboard, in which the knight visits every square without ever landing on the same square twice. This is not the sort of problem XSLT was designed to solve, but by showing that it can be done I hope it will convince you that XSLT has the computational power and flexibility to deal with the many more modest algorithmic challenges that arise in routine day-to-day formatting applications. New features in XSLT 2.0 make this kind of application much easier to write, which means that the stylesheet is almost a total rewrite of the XSLT 1.0 version.

The stylesheet presented in this chapter was written for a practical purpose, not to serve as an example of good programming practice. I wrote in the previous edition of this book that the stylesheet was originally written by Eduardo Gutentag and subsequently modified by James Clark. The stylesheet at that time was around 750 lines long. The current version has grown to over 2,500 lines, and claims as its authors Norman Walsh, Chris Maden, Ben Trafford, Eve Maler, and Henry S.

Thompson. No doubt others have contributed too, and I am grateful to W3C and to these individuals for placing the stylesheet in the public domain. Because the stylesheet has grown so much, and because many of the template rules are quite repetitive, I have omitted much of the detail from this chapter, selecting only those rules where there is something useful to say. But I haven't tried to polish the code for publication-I am presenting the stylesheet as it actually is, warts and all, because this provides many opportunities to discuss the realities of XSLT programming. It gives the opportunity to analyze the code as written and to consider possible ways in which it can be improved. To the individuals whose code I am criticizing, I apologize if this causes them any embarrassment. I do it because I know that all good software engineers value criticism, and these people are all top-class software engineers .

Before embarking on this chapter, I did wonder whether there was any value in presenting in a book about XSLT 2.0 a stylesheet that is written almost entirely using XSLT 1.0. As the chapter progressed, I found that it actually provided a very good opportunity to identify those places where XSLT 2.0 can greatly simplify the code that needs to be written. I hope that it will therefore serve not only as a case study in the use of XSLT 1.0, but also as an introduction to the opportunities offered by the new features in 2.0.