LotusXSL implements an XSL processor in Java that can be used from the command line, in an applet or a servlet, or as a module in other programs. By default, it uses the XML4J XML parser (available as a xerces.jar file when you download LotusXSL) using xerces, but it can interface to any XML parser that conforms to the DOM level 2 or SAX level 1 specification. The freely available LotusXSL used to be a tool developed by alphaWorks, but has now been donated to the Apache project, which maintains it under the name Xalan. LotusXSL is a version (or distribution) of Xalan that has been tested and approved by IBM alphaWorks.

Openwave's software developer kit, UP.SDK, is the leading solution for creating WAP 1.1-compatible Internet services and applications for wireless handsets. The freely available UP.SDK contains the tools and interfaces necessary for a developer to create innovative applications for the wireless Internet.

UP.SDK includes the robust UP.Simulator software, available for Windows platforms and designed to accurately simulate the behavior of a variety of Internet-enabled handsets.

Finally, you need a JVM since LotusXSL is a Java implementation of the XSL engine and needs a container to run.

The primary purpose of this tutorial is to introduce you to the following concepts:

• Transforming an XML document into WML
• Using XSLT, XML, and WML

WAP is published by the WAP Forum, founded in 1997 by Ericsson, Motorola, Nokia, and Unwired Planet. Forum members now represent over 90% of the global handset market, as well as leading infrastructure providers, software developers, and other organizations.

What Is WML?
WML - Wireless Markup Language - is a markup language inherited from HTML, but it's based on XML, so it's much stricter than HTML.

WML is used to create pages that can be displayed in a WAP browser. Pages in WML are called decks, which are constructed as a set of cards. WML is mostly about text. Tags that would slow down the communication with handheld devices are not a part of the WML standard, and the use of tables and images is strongly restricted.

Since WML is an XML application, all tags are case sensitive (<wml> isn't the same as <WML>), and all tags must be properly closed.

When a WML page is accessed from a mobile phone, all the cards in the page are downloaded from the WAP server. Navigation between the cards is done by the phone computer (inside the phone) without any extra access trips to the server. See the Resources section for more information about WAP and WML.

Okay, enough theory stuff...let's gets started!

Recalling Our XML Document
I hope you still remember our XML example (mybooks.xml). To refresh your memory, Listing 1 depicts our XML file. As explained in my previous article, you're free to modify your XML document any way you like, but you'll then have to pay extra attention to some of the details when we get into creating our WML stylesheet.

Note that we won't reference any XSL stylesheet onto our XML document. This is because we'll explicitly plug in our WML, XSL, and XML documents to perform the translation from a command line.

Our goal is to produce a WML page that looks like Figure 1, using UP.SDK simulator software.

Creating the Stylesheet Document
Let's see how we can devise a stylesheet to display the mybooks.xml document nicely on a WML browser. Listing 2 shows a complete XSL file to render our XML file (mybooks.xml) into a WML page. As you can see, it's a bit more complex than our previous XSL document.

Understanding the WML Stylesheet
Let's now take a closer look at our mybooks_wml.xsl stylesheet. The second line of the XSLT stylesheet is:

<xsl:stylesheet version="1.0" xmlns:xsl=
"http://www.w3.org/1999/XSL/Transform">

<xsl:stylesheet xmlns:xsl=
"http://www.w3.org/TR/WD-xsl">

<xsl:output method=
"xml" indent="yes"/>

<xsl:template match="/">

Now we begin to construct the body of our WML page using <wml> tags:

<wml>
<xsl:apply-templates select="//ITEM" />
</wml>

Now we'll start to define those ITEM templates. The <xsl:element> element allows an element to be created with a computed name. The name of the element to be created is specified by a required name attribute (card) and an optional namespace attribute. In other words, this creates the <card> element with attributes id="Book<xsl:number/> and title="My Book Catalog". The element <xsl:number/> is an empty element and serves as a counter.

Similarly, we created the element <do> with the attribute type="accept" and the label="Next Book".

The last element we created is <go> with the attribute name href="#Book<xsl:number value="position() + 1". This translates to #Book2 (since the position of this template is 1).

We close the card and do elements.

The XSL <xsl:value-of> element can be used to select the value of the element matched by the select predicate.

The XSL stylesheet then closes all open element tags in order, with no nesting allowed.

Listing 4 is the second half of our stylesheet.

The XSL <xsl:template match="ITEM[position() = last()]"> checks for the last ITEM element in our XML document. If it actually is the last element, the XSLT processor will continue with the next line; otherwise it will skip and apply <xsl:template match="ITEM"> again. The rest is pretty simple, except for element go attribute <xsl:attribute name="href">#Book<xsl:numbervalue="count(//ITEM) - count(//ITEM) + 1"/></xsl:attribute>.

The XSLT count() function returns the number of nodes in the argument node-set. In our example it returns three (since there are only three books in our XML document). Thus the result is an attribute value of #Book1, which forces the WML browser (or our WAP simulator) to go back to the Book1 card.

I'm sure there are several other and possibly easier ways to create this behavior using other XSLT functions, but I'll leave this as an exercise for the reader.

Performing Your Own Transformations
Both Xalan (LotusXSL) and UP.SDK have an HTML start-up page: readme.html (make sure to read the getting-started link) and upsdk40.html, respectively. They will show you how to set your classpath for the Xalan processor. At a minimum, you must include xalan.jar and xerces.jar on your system class path to perform the translation.

Java.org.apache.xalan.xslt.Process provides a basic utility for performing transformations from the command line. The command line for most standard transformations is as follows:

java org.apache.xalan.xslt.Process -
in xmlSource -xsl stylesheet -
out outputfile

Both mybooks_.xml and mybooks_wml.xsl are saved under gotxslt directory as d:\gotxslt\*.*

To perform the translation, type the following:

D:\>cd gotxslt
D:\gotxslt>java
org.apache.xalan.xslt.Process -in
mybooks.xml -xsl mybooks_wml.xsl
-out mybooks.wml

Testing the Deck In order to test our WML output file, you need to start the UP.Simulator program (upsim.exe) and type the URL of your file (in this case file://d:/gotxsl/mybooks.wml) in the Go field and press Enter. The results of a successful request are shown in Figure 3:

Upon clicking the Next button (which is just below the text labeled "Next Book"), a second card will display the second book. Clicking again for our third book, you'll see that this time the label shows "Back" (see right-hand picture in Figure 3). Clicking on the Next button again will take you to our first book, and the loop will continue.

Conclusion
This article has shown a way to use XML and XSL transformation to create a WAP-compatible WML file. We've just scratched the surface of the potential of WAP/WML. XSLT is a powerful technology that can provide many benefits and hopefully you'll now feel confident to play with other examples on your own.

In Part 3 we'll translate our XML file into VoiceXML.

Resources

• WAP/WML forum: www.wapforum.org/
• LotusXSL: www.alphaworks.ibm.com/tech/LotusXSL
• Apache XML Project: http://xml.apache.org/
• Openwave UP.SDK Software Developer Kit, Release 4.0 or 4.1: http://developer.openwave.com/