XSLT, 2nd Edition

Example: Generating an SVG Pie Chart

As we outlined the functions and operators available in XPath and XSLT, you probably noticed that the mathematical functions at your disposal are rather limited, even in XSLT 2.0. In this example, we’ll write an extension that provides a variety of trigonometric functions. We’ll do this in several ways:

• We’ll use the extension mechanisms in Xalan and Saxon to call static methods in the java.lang.Math class.

• We’ll use the trigonometric functions in the EXSLT math library (more on EXSLT later).

• We’ll use the Bean Scripting Framework, an interesting piece of code from the Apache Jakarta project that lets us write extension functions in a variety of scripting languages, including JRuby, JavaScript, Jython, and Jacl.

• We’ll use classes from the .NET library to extend the Microsoft XSLT processor.

We’ll start this section by building the stylesheet once, and then we’ll discuss what’s different in each iteration. Our scenario is that we want to generate a Scalable Vector Graphics (SVG) pie chart from an XML document. This document contains the sales figures for different stores of a company; we need to calculate the dimensions of the various slices of the pie graph for our SVG document. Here’s the XML source we’ll be working with:

<?xml version="1.0" encoding="utf-8"?>
<!-- chocolate-sales.xml --> <report month="8" year="2006"> <caption> <heading>Chocolate bar sales</heading> <subheading>(units)</subheading> </caption> <store> <name>Carrboro</name> <brand ...