• 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
• Chapter 10: Working with XQuery in Stylus Studio
  • Getting Started with XQuery in Stylus Studio
  • An XQuery Primer
    • What is XQuery For?
    • Your First XQueries
    • Accessing XML Documents with XQuery
    • XQuery and XPath
      • XPath Query Editor
    • Introduction to FLWOR Expressions
    • Generating XML Output with XQuery
    • Accessing Databases with XQuery
  • Understanding FLWOR Expressions
  • Building an XQuery Using the Mapper
  • Working with the XQuery collection() Function
  • Debugging XQuery Documents
  • Creating an XQuery Scenario
  • Generating XQuery Documentation
  • Using XQuery to Invoke a Web Service
  • Generating Java Code for XQuery
• Chapter 11: Composing Web Service Calls
• Chapter 12: Accessing Relational Data as XML
• Chapter 13: Building XML Pipelines
• Chapter 14: Publishing XML Data
• Chapter 15: Integrating with Third-Party File Systems
• Chapter 16: Extending Stylus Studio
• Chapter 17: The Stylus Studio Java API
• Chapter 18: Stylus Studio GUI Reference

Home > Online Product Documentation > Table of Contents > XQuery and XPath

XQuery and XPath

We can access the actors section of videos.xml using this expression: .//actors. When we execute this XQuery we get the following result:

<actors>
               
    <actor id="00000015">Anderson, Jeff</actor>
               
    <actor id="00000030">Bishop, Kevin</actor>
               
    <actor id="0000000f">Bonet, Lisa</actor>
               
    <actor id="00000024">Bowz, Eddie</actor>
               
    <actor id="0000002d">Curry, Tim</actor>
               
    <actor id="00000033">Dullea, Keir</actor>
               
    <actor id="00000042">Fisher, Carrie</actor>
               
    <actor id="00000006">Ford, Harrison</actor>
               
    <actor id="00000045">Foster, Jodie</actor>
               
...etc...
               
</actors>
               

            

That was our first "real" query. If you are familiar with XPath, you might recognize that all the queries so far have been valid XPath expressions. We have used a couple of functions - current-time() and doc() - that might be unfamiliar because they are new in XPath 2.0, which is still only a draft; but the syntax of all the queries so far is plain XPath syntax. In fact, the XQuery language is designed so that every valid XPath expression is also a valid XQuery query.

This means we can write more complex XPath expressions like this one:

              .//actors/actor[ends-with(., 'Lisa')] 
               

            

which gives us this output:

<actor id="0000000f">Bonet, Lisa</actor>
               
<actor id="0000001b">Spoonhauer, Lisa</actor>
               

            

Different systems might display this output in different ways. Technically, the result of this query is a sequence of two element nodes in a tree representation of the source XML document, and there are many ways a system might choose to display such a sequence on the screen. Stylus Studio gives you the choice of a text view, like the one shown above, and a tree view: you use the buttons next to the Preview window to switch from one to the other. Here is what the tree view looks like:

Figure 303. XQuery Preview Window Tree View

This example used another function - ends-with() - that's new in XPath 2.0. We are calling it inside a predicate (the expression between the square brackets), which defines a condition that nodes must satisfy in order to be selected. This XPath expression has two parts: a path .//actors/actor that indicates which elements we are interested in, and a predicate [ends-with(., `Lisa')] that indicates a test that the nodes must satisfy. The predicate is evaluated once for each selected element; within the predicate, the expression " ." (dot) refers to the node that the predicate is testing, that is, the selected actor.

The " /" in the path informally means " go down one level", while the " //" means " go down any number of levels". If the path starts with ". /" or " .//" you can leave out the initial " .". (This assumes that the selection starts from the top of the tree, which is always the case in our examples.) You can also use constructs like " /.." to go up one level, and " /@id" to select an attribute. Again, this is all familiar if you already know XPath.

XPath is capable of doing some pretty powerful selections, and before we move on to XQuery proper, let us look at a more complex example. Suppose we want to find the titles of all the videos featuring an actor whose first name is Lisa. If we look at the videos.xml file, we see that each video in the file is represented by a video element like this one:

<video id="647599251">
               
   <studio></studio>
               
   <director>Francesco Rosi</director>
               
   <actorRef>916503211</actorRef>
               
   <actorRef>916503212</actorRef>
               
   <title>Carmen</title>
               
   <dvd>18</dvd>
               
   <laserdisk></laserdisk>
               
   <laserdisk_stock></laserdisk_stock>
               
   <genre>musical</genre>
               
   <rating>PG</rating>
               
   <runtime>125</runtime>
               
   <user_rating>4</user_rating>
               
   <summary>A fine screen adaptation of Bizet's popular opera.</summary>
               
   <details>Placido Domingo does it again, this time in Bizet's popular opera.</details>
               
   <vhs>15</vhs>
               
   <beta_stock></beta_stock>
               
   <year>1984</year>
               
   <vhs_stock>88</vhs_stock>
               
   <dvd_stock>22</dvd_stock>
               
   <beta></beta>
               
</video>
               

            

The query required to provide the results we desire is written like this:

//video[actorRef=//actors/actor[ends-with(., 'Lisa')]/@id]/title 
               

            

Again, this is pure XPath (and therefore a valid XQuery). You can read it from left-to-right as:

When run against our source document, the result of this XQuery is:

<title>Enemy of the State</title>
               
<title>Clerks</title>
               

            

Many people find that at this level of complexity, XPath syntax gets rather mind-boggling. In fact, this example just about stretches XPath to its limits. For this kind of query, and for anything more complicated, XQuery syntax comes into its own. But it is worth remembering that there are many simple things you can do with XPath alone, and that every valid XPath expression is also valid in XQuery.

XPath Query Editor

Stylus Studio provides a built-in XPath Query Editor in its XML Editor that allows you to visually edit and test complex XPath expressions, and it supports both version 1.0 and 2.0.

Figure 304. XPath Query Editor

See Using the XPath Query Editor to learn more about using this tool.