Professional XSL

Professional XSL

by CAGLE, Andrew Watt, Jeni Tennison, Paul Tchistopolskii
     
 

Professional XSL takes an applied, tutorial-style approach to teaching the core fundamentals of the XSLT, XPath and XSL-FO specifications. You'll learn how to create well structured and modularized stylesheets to generate your required output, how to change, filter, and sort data, and how to incorporate other content for presentation purposes.

XML is

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Overview

Professional XSL takes an applied, tutorial-style approach to teaching the core fundamentals of the XSLT, XPath and XSL-FO specifications. You'll learn how to create well structured and modularized stylesheets to generate your required output, how to change, filter, and sort data, and how to incorporate other content for presentation purposes.

XML is now the established standard for platform-neutral data storage and exchange, separating content from presentation. Its popularity is due to the flexibility of the language and the ability to reuse the data in a variety of ways. XSL is a key technology for working with XML, and is comprised of two parts: XSLT is the official language for transforming XML from one format to another, whether for restructuring/selectively processing the data or presenting the data for display; XSL-FO is a proposed vocabulary for incorporating information concerning how the document should be arranged for presentation. A related standard, XPath, is the language for addressing specific parts of an XML document.

Who is this book for?

This book is ideal for developers who have a good understanding of XML data and its structure, and who need to transform the data or apply styling for business-to-business and web applications.

What does this book cover?

  • Explains what XSL is and what it is for
  • Describes the XPath language for specifying locations in an XML tree
  • XSLT basics - the core features of the language sufficient for creating most applications
  • Advanced XSLT - additional features and techniques to enhance and improve your applications
  • Demonstrates common structural transformations
  • Demonstrates transforming XML for display (including HTML, Word, PDF, WML, VoiceXML, and SVG/VML formats)
  • Concepts and key elements of CSS and XSL-FO
  • Working with XSLT and XML Schemas

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Product Details

ISBN-13:
9781861003577
Publisher:
Wrox Press, Inc.
Publication date:
05/01/2001
Series:
Professional Ser.
Pages:
808
Product dimensions:
7.28(w) x 9.16(h) x 1.69(d)

Read an Excerpt

Chapter 3: XSLT Basics

In this chapter, we will build on Chapters 1 and 2 to provide you with enough information to start building useful XSLT stylesheets. I will introduce a number of the elements that make up the language, providing examples of their use. We will also look at a few of the functions built into the language and see how XSLT manages namespaces, whitespace and some other important issues.

To illustrate the concepts I introduce, we will work mainly with two documents, one that is textual in content, and one that is more data oriented. The former is a Shakespeare play (Hamlet), and the latter is a book catalog that could, for example, have been extracted from a relational database. Both documents are given in the code download for the chapter.

By the end of the chapter, you will:

  • have a clearer picture of the processing model of XSLT
  • know the difference between push and pull model stylesheets, and when to use each
  • understand the use of the most important XSLT elements
  • understand the use of a few of the built-in functions
  • understand the basic rules of how XSLT copes when there are conflicts in the stylesheet
  • know more about the built-in template rules and how to over ride them

XSLT Processing

Before delving into the detail of XSLT elements and functions, let's start by looking in detail at how an XSLT processor, such as XT, Saxon or MSXML3, processes a document. We will look at the model from an abstract view � becoming an XSLT processor ourselves and working our way through a document and stylesheet. We'll then look at the two fundamental ways in which this model can be used.

More information on these processors can be found in Appendix E. Later in this chapter I will be mainly using XT to process XSLT stylesheets, but any of these processors can be used. XT is similar in use to Instant Saxon, which was introduced in Chapter 2.

The XSLT Processing Model

Although we often talk of an XSLT processor as something that turns one XML document into another (or into an HTML or text document), this is not strictly true. The specification actually talks in terms of a source tree (or input tree) and a result tree. There is therefore an assumption that, for example, if we are starting from a text document rather than an existing DOM tree, it has been turned into some sort of tree structure before the XSLT processor starts its work, and that the result tree will be used for further processing or serialized in some way to create another text document.

The model, including formatting, therefore looks like this...

...This concept is simple enough. But you will have read in Chapter 1 that XSLT is a declarative language and uses templates. How does this work in practice? Let's have a look at a simple XML document and stylesheet, and walk through the processing.

Processing a Document

Here is my XML document � it is the book catalog that you will be familiar with if you have read Professional XML (Wrox Press, ISBN 1-861003-11-0), although I have cut it down to just two books, removed some elements and renamed it shortcatalog.xml:
<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<Catalog>
<Book>
<Title>Designing Distributed Applications</Title>
<Authors>
<Author>Stephen Mohr</Author>
</Authors>
<PubDate>May 1999</PubDate>
<ISBN>1-861002-27-0</ISBN>
<Price>$49.99</Price>
</Book>
<Book>
<Title>Professional ASP 3.0</Title>
<Authors>
<Author>Alex Homer</Author>
<Author>Brian Francis</Author>
<Author>David Sussman</Author>
</Authors>
<PubDate>October 1999</PubDate>
<ISBN>1-861002-61-0</ISBN>
<Price>$59.99</Price>
</Book>
</Catalog>

We'll look at the XSLT stylesheet we use to transform this document shortly, but let's now become an XSLT processor and see what happens. We already know that, as an XSLT processor, we cannot use the source XML, but need a tree representation based on the structure and content of the document. So here it is...

...Each node is described by a block of three rectangles. In the top rectangle is the node type, with the node name in the rectangle below it. The bottom rectangle contains an asterisk if the node has element content, and the text if it has text content.

At the top of the tree is the root node or document root. Don't confuse this with the root element (or document element) familiar from XML. The document root is the base of the document, and has the document element (<Catalog>) as a child. It also has the XML declaration and any other top-level nodes (which might be comments or processing instructions) as children. The document element contains two child <Book> elements, and these hold the information about the books.

So now we have the tree structure, we can start to populate and process it. This is the processing model we will use...

Before XSL processing starts, both the source document and XSLT stylesheet must be loaded into the processor's memory. How this happens is dependent on the implementation. One option is that both are loaded as DOM documents under the control of a program. Another option is that the stylesheet is referenced by a processing instruction in the source XML document. IE5 can operate in this way, and will automatically load the stylesheet when the XML document is loaded.

And here is the XSLT stylesheet (TitleAndDate.xsl) we will use to process the shortcatalog.xml to get a new XML document listing just the titles of the books and their publication dates:

<?xml version="1.0" encoding="utf-8" standalone="yes"?>
<xsl:stylesheet
version="1.0"
xmlns:xsl="http://www.w3.org/1999/XSL/Transform">
<xsl:template match="/">
<xsl:apply-templates/>
</xsl:template>
<xsl:template match="Catalog">
<Books>
<xsl:apply-templates/>
</Books>
</xsl:template>
<xsl:template match="Book">
<Book>
<xsl:value-of select="Title"/>, <xsl:value-of select="PubDate"/>
</Book>
</xsl:template>
</xsl:stylesheet>

Once the documents are in memory, we can start our processing. The XSL processor starts by reading the template for the document root from the stylesheet (step 1). Here is that template:

<xsl:template match="/">
<xsl:apply-templates/>
</xsl:template>

The first line indicates that it is a template, with a match attribute to indicate the node or nodes it is matching. The attribute value is an XPath expression, in this case just being the / to indicate the document root.

Working round the diagram, at step 2 we find the source node (strictly, the node-set, but here it will comprise a single node) in the source tree that the template matches. This will be the document root.

The second line of the template moves us on to step 3 and indicates that we will execute whatever templates apply to the children of this node. The document root has two children � the XML declaration and the <Catalog> element.

Looking through the stylesheet, there is no template for the XML declaration (XSLT does not give us access to this node), but there is one for the element. Processing a document using XSL is a recursive process, and we are now back to step 1 with a new template. Here is the template:

<xsl:template match="Catalog">
<Books>
<xsl:apply-templates/>
</Books>
</xsl:template>

This contains some text, which looks like another element called <Books>. As our diagram indicates, we will transform this into a result node at step 3. It also contains an <xsl:apply-templates/> instruction, so we will again look for templates to execute matching the child nodes.

The only children of the <Catalog> element are the two <Book> elements, so we will read the template for these elements and go round the circle again. Here is the template...

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