Tutorial: Using XQuery in ASP.NET Table of Contents Tutorial: Using XQuery in ASP.NET_________________________________________1 Table of Contents_____________________________________________________1 Introduction_____________________________________________________________2 What is XQuery?_________________________________________________________2 XQuery and ASP.NET_____________________________________________________4 MS XQuery Demo________________________________________________________4 XQuery's relation with System.Xml_______________________________________5 The XQueryNavigator class______________________________________________5 The XQueryDocument class_____________________________________________5 The XQueryNavigatorCollection class_____________________________________5 The XQueryExpression class_____________________________________________5 The XQueryException class______________________________________________5 Putting it all together___________________________________________________5 XQuery Expression Tester_________________________________________________7 Creating the project____________________________________________________7 Adding the reference___________________________________________________7 Building and running the application______________________________________7 The XML source document______________________________________________8 The XSL Stylesheet_____________________________________________________9 XQuery's syntax and examples_____________________________________________13 Primary Expressions__________________________________________________13 Path Expressions______________________________________________________13 Worksheet 1: Path Expression examples__________________________________13 Sequence Expressions__________________________________________________14 Worksheet 2: Sequence Expression examples______________________________14 Arithmetic Expressions________________________________________________14 Worksheet 3: Arithmetic Expression examples_____________________________14 Comparison Expressions_______________________________________________15 Worksheet 4: Comparison Expression examples____________________________15 Logical Expressions___________________________________________________15
Worksheet 5: Logical Expression examples________________________________15 Constructors_________________________________________________________15 Worksheet 6: Constructor examples______________________________________16 FLWR Expressions____________________________________________________16 Worksheet 7: FLWR Expression examples________________________________16 Sorting Expressions___________________________________________________17 Worksheet 8: Sorting Expression examples________________________________17 Conditional Expressions________________________________________________17 Worksheet 9: Conditional Expression examples____________________________17 Quantified Expressions________________________________________________18 Worksheet 10: Quantified Expression examples____________________________18 Expressions on Datatypes_______________________________________________18 Worksheet 11: Expression on Datatypes examples__________________________18 Validate Expressions__________________________________________________18 Worksheet 12: Validate Expression examples______________________________18 Code explanation_____________________________________________________19 Wrap-up_______________________________________________________________21
Introduction This tutorial will introduce you to XQuery and help you how to use it in ASP.NET. It starts with explaining what XQuery is and its purpose besides current query languages like XPath and XSLT. Then we'll move on to look at some simple XQuery Expressions. We'll see how they are constructed and what results they should obtain given an example XML source document. We'll see that these expressions are extremely readable and easy to write. You will be able to play with XQuery Expressions yourself, using a simple ASP.NET C# Web Application. It is assumed that you know the basics of how to use VS.NET (creating a new project, adding references to a project, programming in code-behind mode, etc.).
What is XQuery? XQuery is a new XML Query Language, which is a work in progress by the XML Query Working Group of the W3C. It has currently the W3C Working Draft status, but is due to reach W3C Recommendation status before the end of this year.
Where does XQuery stand in the jungle of XML related languages? Well, we could visualize this roughly as follows (note that no complete overview is pretended, for the sake of simplicity): Timely ordered
XML 1.0
XPath 1.0
XSLT 1.0 XSL 1.0
XSL-FO XML Schema
XPath 2.0
XQuery 1.0
XSLT 2.0
Fig. 1: XQuery's relation to other W3C XML related specifications In the above diagram we see some specifications above the dashed line - these are W3C Recommendations. The specifications below the dashed line are currently what the W3C calls "Works in Progress"; as you can see, XQuery is one of them. Furthermore, we see that XPath 1.0 first was a part of XSL 1.0 but grew out later on as a fully separate specification. The main reason for that is that XPath is being reused in other W3C specifications. XQuery is a strongly typed language, and its data type system is based on XML Schema (http://www.w3.org/XML/Schema). It is also tightly related to XPath 2.0: XQuery is actually a superset of XPath 2.0. XPath 2.0 is also used by the upcoming XSLT 2.0 specification, which means that XSLT 2.0 will also be a superset of XPath 2.0. Whereas XSLT is a transforming language and is single document based, XQuery is more a querying language, which is multiple document based and is more suitable for big XML source documents. In the end, both will co-exist, and each one will cover different areas of possible applications, but also will share some overlap in certain areas, of course. XQuery will have support for updating the data source, whether it is a file on disk, or a database table. It will use a SQL-like syntax for doing this. This support could still be integrated in the
first upcoming W3C Recommendation, but it is more likely that it will be postponed to a later version, as there are still many issues to resolve. You can read up more detailed on the subject at: http://www.w3.org/XML/Query. If you intend to do this, the first document you should read is "XQuery 1.0: An XML Query Language", available at: http://www.w3.org/TR/xquery/. That document will give you a general idea what XQuery has to offer without going into too much detail. XQuery is basically a set of XQuery Expression types, which make up a query. We'll see some basic examples of them a bit later on. From now on, in the context of this tutorial, let's call an XQuery Expression simply an xquery.
XQuery and ASP.NET As you may know, ASP.NET basically has the System.Xml namespace supporting the use of XML in .NET code. The MS XQuery Demo managed class set adds the capability to use XQuery in conjunction with System.Xml and other .NET classes. We'll go into this early XQuery implementation a bit further on. To run an xquery in ASP.NET, you need at least an XML source document, be it a file on disk, or a dynamically generated one. The important thing to remember here is that the XML source needs to be well formed. Valid is not required here, but you could always validate the XML prior to applying it an xquery, of course. Then, you would need to write your xquery to run over one or more input XML source documents. To augment your understanding of how it all works, let us now first see what exactly is MS XQuery Demo before we move on to creating a test page in ASP.NET and run some basic xqueries.
MS XQuery Demo As said, the implementation that Microsoft developed is called MS XQuery Demo, and can be found at http://xqueryservices.com. MS XQuery Demo basically consists of two parts. One is the web site demo test page. You can use this page to interactively test your xqueries. The xqueries are run over fixed XML source documents – they are not modifiable. The other part, which we are going to use here, is a downloadable managed .NET class set. Now, go ahead, and download and install this first; you can get it at http://xqueryservices.com/Setup/xquery.msi. This managed class set let's you run your xqueries over your own XML source documents, be it one single document, or multiple ones.
XQuery's relation with System.Xml The MS XQuery managed classes reside in the namespace Microsoft.Xml.XQuery. They are designed for use with the existing classes in the System.Xml namespace. The managed classes in MS XQuery are: XQueryNavigator, XQueryDocument, XQueryNavigatorCollection, XQueryExpression, and XQueryException. Let's have a look at each one of them now. The XQueryNavigator class XQueryNavigator
This class is used to create an XML object for navigation.
The XQueryDocument class XQueryDocument
This class provides an XML object to run xqueries over.
The XQueryNavigatorCollection class XQueryNavigatorCollection
A collection of XQueryNavigator objects to run xqueries over.
The XQueryExpression class XQueryExpression
This class provides an object, which encapsulates the XQuery Expression – it is parsed, checked for any syntax error, and finally compiled. Then it is ready to be run over the navigator collection of XQueryNavigators.
The XQueryException class XQueryException
This class provides for any exception thrown by the XQuery classes.
Putting it all together The classes needed to run an xquery are basically XQueryNavigator, XQueryNavigatorCollection, and XQueryExpression. How they interrelate can best be shown as follows:
XQueryDocument
XQueryNavigator XQueryNavigatorCollection
XML source
XQueryExpression
document XQueryException
XQueryNavigator
.ToXML()
Fig. 2: MS XQuery Demo managed class set In the above diagram we see that the XQueryNavigatorCollection is a collection of XQueryNavigator classes. Each XQueryNavigator represents a set of data. We'll call them simply navigators here. The XQueryExpression contains the xquery. This xquery defines the target navigators to run the xquery over, as we'll see later on in the example section. But first, to be able to run xqueries, in the next section we'll be creating a simple xquery tester, which later is used to run various xqueries over a basic and simple XML source document, to show you a series of basic xqueries.
XQuery Expression Tester In this section, we'll create a simple ASP.NET web form letting the user cut and paste their XML source in a textbox, and then copy and paste the xquery and run it using the MS XQuery .NET Managed class set. The resulting output is shown using the XML Web Control, after having it applied an XSL Stylesheet, to display the results in a more neat and readable XML format.
Creating the project Creating the project is simple. Start VS.NET and click the New Project link on the start page. Choose Visual C# Projects, and in the right pane, choose ASP.NET Web Application. Enter its name, "XQueryTester". Click OK and wait until the classes are created. Then, delete "WebForm1.aspx" and add the page "XQT.aspx" from the download material (note that if you're not using VS's Solution Explorer to do this you also need to copy the "XQT.aspx.cs" file).
Adding the reference Then, add a Reference to the project by choosing the menu "Poject | Add Reference". In the .NET tab, select the file named "Microsoft.Xml.XQuery.dll", and click the button "Select". Finally, click OK. The reference should appear in the Solution Explorer, under the References directory. Press Ctrl+Alt+L if you do not see the Solution Explorer. Next, add a new project subdirectory called "xsl", and add the file "xqt.xsl". This is the XSL Stylesheet that is used to format the xquery results.
Building and running the application You'll need to choose a Start Up file before compiling and running your application. Choose "Set as Start Up Page" on "XQT.aspx" by right-clicking the project name in the Solution Explorer window pane, and then finally press F5. After compiling the project, and activating the debugging environment, the following screen should turn up:
Fig. 3: Screenshot of XQueryTester's opening window
If you run into trouble, try re-reading the section to see if you didn't miss something. If you do not succeed in getting the project to work, you can try to copy the whole project from the download material to your web root, activate the web application using the Internet Services Manager (ISM), and run the application. You may need to change the web root if yours is different, and also the reference may need to be added again if the path is incorrect. OK, now you should be able to enter your XML source, and run some simple xqueries over it. The next section will guide you in doing that, and will give you a good feeling of what XQuery can do and how you should write xqueries. After having run some xqueries using some of the most important XQuery Expression types, you'll quickly get the hang of constructing simple xqueries. Then, after that section is over, we'll be looking in detail at how the code behind the web form works.
The XML source document The XML source file we'll use throughout this section of the tutorial is as follows:
T000001 Introduction to XQuery Introduction XQuery is an XML query language. Body XQuery has a pleasant to use syntax. The human-readable form is actually not XML, but it does produce XML, if properly written.The language has a host of expression types, called XQuery Expressions. One of the most powerful XQuery Expression is called the FLWR (pronounced 'flower') expression. Resumen XQuery is new and complete XML querying language, likely to get very popular in the coming years. T000002 XQuery's Syntax Introduction
XQuery has two syntax forms: one is the human-readable called XQuery, the other one is its XML counterpart and is called XQueryX. Body In this tutorial we'll only look closer at the human-readable version of XQuery. It is called human-readable because it is designed to be highly readable by humans, and is easy to write. The language consists basically of a set of expression types. Resumen In this tutorial we had a closer look at the human-readable syntax form of XQuery. T000003 XQuery: Advanced Tricks Introduction In this section we'll talk about some advanced XQuery tricks. Body The first advanced trick we'll look at is the use of nested FLWR expressions. You can compare this with a relational database query where you use the UNION keyword to combine results from tables in one resulting table. Resumen XQuery allows for some cool and advanced querying tricks.
The XSL Stylesheet Note that the used XSL Stylesheet to present the resulting XML was originally written by Jason Patterson at SnippetCentral at TopXML.com (http://www.topxml.com/snippetcentral/main.asp? view=viewsnippet&lang=&id=v20010305161458). All the credit of this very useful script goes to him. The script used in this tutorial is an updated version he personally sent me, and is not modified by me in any way. Jason also indicated that he's going to update the site's script real soon, which is great news – it may already be there when you read this.
The stylesheet is as follows:
font:10pt 'Verdana'; 0em; color:blue; color:#990000; color:gray; color:green; color:black; color:red 
