Beginning XML, 5th Edition

Chapter 11

Event-Driven Programming

WHAT YOU WILL LEARN IN THIS CHAPTER:

• Necessity of XML data access methods: SAX and .NET’s XMLReader
• Why SAX and XMLReader are considered event-driven methods
• How to use SAX and XMLReader
• The right time to choose one of these methods to process your XML

There are many ways to extract information from an XML document. You’ve already seen how to use the document object model and XPath; both of these methods can be used to find any relevant item of data. Additionally, in Chapter 12 you’ll meet LINQ to XML, Microsoft’s latest attempt to incorporate XML data retrieval in its universal data access strategy.

Given the wide variety of methods already available, you may be wondering why you need more, and why in particular do you need event-driven methods? The main answer is because of memory limitations. Other XML processing methods require that the whole XML document be loaded into memory (that is, RAM) before any processing can take place. Because XML documents typically use up to four times more RAM than the size of the file containing the document, some documents can take up more RAM than is available on a computer; it is therefore necessary to find an alternative method to extract data. This is where event-driven paradigms come into play. Instead of loading the complete file into memory, the file is processed in sequence. There are two ways to do this: SAX and .NET’s XMLReader. Both are covered in this chapter.

UNDERSTANDING SEQUENTIAL PROCESSING ...