Chapter 6. Using XPath Queries

Throughout this book,whenever we mention or implement XPath expressions, we use what is called the abbreviated form. In this chapter, we will learn the parts that Microsoft supports of an enhanced syntax, called the verbose form of XPath. Yes, that's right. Microsoft has implemented only a subset of the query language. Also, there are some differences between Microsoft's implementation and the original W3C specification. We'll cover these topics first thing.

We'll be discussing things like selection predicates, node tests, and axes and how these are combined to form location paths . You'll have plenty of examples, as usual, along the way to verify your understanding of the subject matter.

Let's first look at implementation limitations and then at the differences between Microsoft's implementation and the W3C standard.

This chapter will cover the following topics:

• Microsoft's adaptation of the W3C XPath requirements and its limitations

• XPath data types and processes, such as conversion of these data types and mapping between XDR schema and XPath data types

• The SQL Server 2000 CONVERT function and its use in implicit conversions

• Location paths and their components : node tests, axes, and predicates

• Boolean, arithmetic, relational, and equality operators and how they are used in selection predicates

• Accessing database objects and the limited functionality this process provides