• Chapter 1: Getting Started with Stylus Studio
• Chapter 2: Editing and Querying XML
• Chapter 3: Converting Non-XML Files to XML
• Chapter 4: Working with XSLT
• Chapter 5: Creating XSLT Using the XSLT Mapper
• Chapter 6: Debugging Stylesheets
• Chapter 7: Defining XML Schemas
• Chapter 8: Defining Document Type Definitions
• Chapter 9: Writing XPath Expressions
  • About the XPath Processor
  • Sample Data for Examples and Testing
  • Getting Started with Queries
  • Specifying the Nodes to Evaluate
  • Handling Strings and Text
  • Specifying Boolean Expressions and Functions
  • Specifying Number Operations and Functions
  • Comparing Values
  • Finding a Particular Node
  • Obtaining a Union
  • Obtaining Information About a Node or a Node Set
  • Using XPath Expressions in Stylesheets
  • Accessing Other Documents During Query Execution
  • XPath Quick Reference
• Chapter 10: Working with XQuery in Stylus Studio
• Chapter 11: Composing Web Service Calls
• Chapter 12: Accessing Relational Data as XML
• Chapter 13: Extending Stylus Studio
• Chapter 14: Stylus Studio Reference

Home > Online Product Documentation > Table of Contents > How the XPath Processor Evaluates Comparisons

How the XPath Processor Evaluates Comparisons

A query can compare values of elements. For example:

last-name [. = "foo"] 
               

            

The XPath processor compares the value of each last-name element in the current context with the value "foo". The result of each comparison is a Boolean value. The XPath processor returns the last-name elements for which the comparison yields true.

As mentioned before in Filtering Results of Queries, the XPath processor evaluates filters with respect to a context. For example, the expression book[author] means for every book element that is found, determine whether it has an author child element. Likewise, book[author = "Bob"] means for every book element that is found, determine whether it contains an author child element whose value is "Bob".

Comparisons are case sensitive. For example, "Bob" and "bob" are not considered to be equal.

Remember that comparisons return Boolean values. For example:

/bookstore/book/author/last-name="Bob"
               

            

You might think that this query returns authors whose last name is "Bob". But this is not the case. This query returns a single Boolean value. It tests each last-name element to determine if its value is "Bob". As soon as the XPath processor finds a last-name element that tests true, it returns true. If no nodes test true, this query returns false.

To obtain author elements whose last name is "Bob", enclose the comparison in a filter as follows:

/bookstore/book/author[last-name="Bob"]