|By Steve Hoenisch||
|February 22, 2002 12:00 AM EST||
The power and elegance of XSLT - the Extensible Stylesheet Language for Transformations - stems from its ability to transform XML documents into other output formats like HTML, fulfilling one of the original promises of XML: separating content from presentation.
XSLT is particularly powerful because a single stylesheet can format all the XML documents conforming to a DTD into HTML for publication on a Web site. The stylesheet can also be used to automatically generate such features as a hyperlinked table of contents, the building of which requires substantial manual work without XML.
XSLT is also elegant, because if you need to reformat all the pages in your Web site, for instance, you need to change the code in only one place, the stylesheet, so long as your source documents are in XML.
Written primarily for content authors, technical writers, Web designers, and other nonprogrammers, this tutorial aims to demonstrate some of XSLT's power and elegance in separating content from presentation and in automatically generating narrative-oriented HTML documents while showing you how to create progressively more complex template rules - rules that are at the core of XSLT.
Review: The Template Rule
In its most basic form an XSLT stylesheet uses what are called template rules to match nodes in an XML document and transform them into another format. A template rule is an XSL element that matches a node in the XML source document and typically applies an output format, such as HTML, to it. For example, say you have the following simple XML document:
<?xml version="1.0"?>You can use a template rule to find the children of the root element and to format its contents in HTML for presentation. Here's a template rule that does just that:
<body>You've probably heard the
propaganda by now: XML blesses you
with a way to separate content from
<xsl:template match="/">In this rule the <xsl:template match ="/"> element uses the value of its match attribute to find a node in the XML source. The forward slash operator, an XPath expression, specifies the document's root node. The rule could also match on the same node by specifying it explicitly in the template rule, that is, <xsl:template match="document">. By matching on the root node of the document, we're able to build an HTML container that provides the skeleton code (here, just <html> and <body>) for our document. I'll expand on this concept below.
The <xsl:apply-templates> element invokes a built-in XSLT template rule that processes the children of the matched node, meaning roughly that it outputs the children. Because there's only one child of the <document> node in our XML file, <xsl:apply-templates> suffices to print the meager contents of the file. If, however, the <document> element contained more children, <xsl:apply-templates> would print all of them out, too, and we'd want additional template rules to control how they're formatted.
Before we can push our source XML and its accompanying stylesheet through an XSLT processor to render the HTML output, we need to do a couple more things. First, we need to add an XML processing instruction to the top of the stylesheet. Second, we must wrap the template rule with the <xsl:stylesheet> element, which all XSL stylesheets require as their top-level element, and set a namespace for it (note that some versions of Internet Explorer and the MSXML parser may require a different namespace; see
http:// msdn.microsoft.com/ and the Unofficial MSXML XSLT FAQ
at www.netcrucible.com/xslt/msxml-faq.htm for details):
<?xml version="1.0"?>We now have a minimal stylesheet that will convert our XML source to HTML. To view the output in Internet Explorer 5.5 or later, we first need to make a change to the XML source document: it must include a stylesheet processing instruction (appended after the XML processing instruction) that references our new minimal stylesheet. In this case it's located in the same directory as the source file, as the path in the href attribute's value testifies:
Let's expand our minimal stylesheet to do a few more things. First, we'll modify our template rule to output the body element specifically (as opposed to all the children of the root element); second, we'll add a link to a Cascading Style Sheet that specifies the visual properties of our HTML formatting:
<?xml:stylesheet type="text/xsl" href="my_stylesheet.xsl"?>
<body>You've probably heard the
propaganda by now: XML blesses you
with a way to separate content from
<?xml version="1.0"?>This stylesheet first matches the root node explicitly by name (document), builds an HTML container for it as before, and then uses the <xsl:value-of> element to select and output the text contents of the message node. The select attribute identifies the element whose contents are to be processed.
"http://www.w3.org/1999/XSL/Transform" version="1.0" >
Notice that in the stylesheet I also added a link to a CSS file in the same directory as the XSLT stylesheet. The CSS file contains the code in Listing 1 (all listings can be found at www.sys-con.com/xml/sourcec.cfm). In this example only a few of the CSS rules are used, but the rest of them will be put into play as we expand our rudimentary stylesheet to process a more complex XML document.
Using CSS to complement XSLT is a powerful strategy for building Web pages - a strategy that splits presentation into what I call formatting and styling. Formatting can be seen to include basic HTML markup like headings, horizontal rules, lists, and the like. Styling, meantime, defines the visual properties of markup: its colors, sizes, widths, margins, bullet types, and so forth. Separating visual styling from formatting gives you a way to make wholesale design changes to a Web site without having to change the formatting code in every HTML document; if you've set up your Web pages properly, with all of them linking to a single CSS, you merely make the stylistic changes in one file, the Cascading Style Sheet.
Building a Complex Stylesheet
This section builds on the review above to create an XSLT stylesheet that will transform any document that conforms to our DTD into an HTML document. We'll create the stylesheet from the top down, step by step, explicating most of the template rules as we go.
Consider the generic XML document in Listing 2.
The document is based on the DTD in Listing 3. (This DTD is very loosely based on a scaled-down version of the TEI Lite DTD with some XHTML and other customizations thrown in; it's been constructed to demonstrate the XSL transformations in this tutorial and, unlike TEI Lite, isn't suitable for other uses. For information about TEI Lite see www.tei-c.org/.)
The XSLT stylesheet in Listing 4 is also based on the DTD. Why bring a DTD into this discussion? The answer is that it's best to build the stylesheet based on your DTD to ensure that all elements and attributes are processed fully and according to your requirements. The DTD provides the cues by which you build your stylesheet. That is, to build a suitable stylesheet - one that processes all the elements and attributes in your XML document fully and appropriately - you should develop your stylesheet based on your DTD, not on an XML document alone. For more information about analyzing DTDs to develop stylesheets, see Chapter 21, "DTD Analysis," in The XSL Companion, by Neil Bradley (Addison-Wesley).
Let's start building the stylesheet. Since XSL stylesheets are themselves XML documents, they should generally begin with an XML processing instruction as their first line: <?xml version="1.0"?>. The next line contains an optional document type declaration for the stylesheet to specify the stylesheet's root element, xsl:stylesheet. I'm including the document type declaration in our stylesheet because I want to declare several general entities as an internal DTD subset for use in the stylesheet. (Recall that general entities let you replace an entity with its value; that is, wherever the entity pub.date appears in the stylesheet as text, it is replaced by its value as defined in the entity declaration, here February 8, 2002.)
<!DOCTYPE xsl:stylesheet [The root element for an XSLT stylesheet must be either xsl:stylesheet or xsl:transform. The xsl: prefix before stylesheet and transform is the customary XSL namespace; all the XSL elements are in the www.w3.org/1999/XSL/Transform namespace, which must be referenced as the value of the xmlns:xsl attribute of the xsl:stylesheet root element, as I've done here (see the chapter titled "XSL Transformations" in O'Reilly's XML in a Nutshell for additional information about the namespace):
<!ENTITY pub.date "February 8, 2002">
<!ENTITY mdash "--">
<!ENTITY nbsp " ">
<xsl:stylesheet xmlns:xsl=Next, I set the output method to HTML and include a reference to the HTML version I want to use:
<xsl:output method=Creating an HTML Container
HTML 4.0 Transitional//EN"/>
Now, bringing a simple template-matching rule into play, we begin building the HTML skeleton for the output file:
<xsl:template match= "document">[...HTML SKELETON CODE...]</xsl:template>This template rule selects the XML document's root element, <document>, and circumfuses it with HTML code, forming a skeleton that will contain the body of the XML document. In the case of this stylesheet, the skeleton is in the form of a header, a content area, and a footer.
In the header I've used an XSL element - <xsl:value-of select="docinfo/title"/> - to select the title of the XML document and to output it in the title slot of the HTML document that I'm building.
Notice, too, that between the HTML <head> tags I've also created an HTML link to a Cascading Style Sheet, which contains as much of the styling information for my HTML formatting as possible:
<link rel="stylesheet" type="text/css" href="doc.css"/>In the next XSL command I again select the value of the <title> tag in the XML document, this time for use as a headline atop the HTML document:
<xsl:value-of select=Skip over the rest of the HTML code in the header now and bore into the content area until you find the next command prefaced by the XSL namespace:
<xsl:apply-templates select="body"/>This template rule selects the entire content of the body element in the XML document, processes it according to the other template rules in the stylesheet, and outputs the result at the point of this command inside the HTML container that we built when we matched on the root element earlier.
Formatting the Body
To format the body of the XML document, my stylesheet includes a template rule that selects the body element: <xsl:template match="body">. This template does three things:
- It inserts a Table of Contents headline.
- It calls another template that dynamically builds a table of contents.
- It processes all <div1> elements.
The <xsl:call-template name="toc"/> command calls a macro (located toward the end of the stylesheet in the Macros section) that cycles through the six levels of <div> elements, makes a reference to the <div> element's heading in the form of a hyperlink, and numbers the section headings using the 1.1 format. (You can see what the output looks like by downloading the XML source document from the XML-Journal Web site and opening it in Internet Explorer 5.5; the hyperlinks in the displayed document are brown but aren't underlined.)
The set of macros that build the table of contents originated in the W3C's XSLT stylesheet for the XML Recommendation. Reverse engineering it is a potent method of teaching yourself some of the advanced capabilities of XSLT. The W3C's stylesheet is available in the download file for Chapter 9 of Michael Kay's book, XSLT Programmer's Reference, at www.wrox.com/. In IE5.0 or greater you can view the XML source code for the W3C's XML Recommendation at www.w3.org/TR/2000/REC-xml-20001006.xml or you can download it and view it using an editor like XML Spy.
The next set of templates in our stylesheet creates headings for the <div> elements, mapping the <head> element in <div1> to the HTML heading element <h1> and so forth through <div6> and <h6>. The template-matching rules for the head elements also call another template, named "head", which inserts an ID attribute in each heading and numbers them with the command mode="number".
Processing the Child Nodes
Finally, after building the table of contents and the headings for each <div> section, the stylesheet uses the following code to process all the children of the <div1> element:
<xsl:template match="div1">In this code the <xsl:apply-templates/> simply tells the XSLT processor to process all the child elements of <div1> and to output them according to the template rules for each child element listed further down in the stylesheet. Many of these child elements are processed simply by what I've called the XHTML Quick Print Module. This template rule selects any of the elements listed in the value of the match attribute, makes a copy of the element, makes a copy of all the element's attributes, and passes them through to the target output file intact. Because my DTD contains several XHTML elements for low-lying nodes, I can use this template rule instead of writing a separate one for each XHTML element.
The complete stylesheet is presented in Listing 4.
On the heels of this column's terse introduction to XSLT, I suggest you spend a couple hours in your neighborhood bookstore reading the following chapters in this order:
- Chapter 6, "Transformation: Repurposing Documents," in O'Reilly's Learning XML
- Chapter 8, "XSL Transformations," in O'Reilly's XML in a Nutshell
- Whatever selections you deem useful from Wrox's XSLT Programmer's Reference by Michael Kay
Finally, take some time to browse through the resources listed on the World Wide Web Consortium's XSL page at www.w3.org/Style/XSL/. The page includes links to other tutorials, a FAQ, the XSL specifications, and a variety of resources.
I also suggest you start playing around with XSLT a little on your own; it's the best way to learn how to use it. Try playing with the code accompanying this column: add some elements to the DTD and the XML document and then write template-matching rules to process and output them in Internet Explorer. You may have to install the newest version of the MSXML parser to get the code to display correctly; see http://msdn.microsoft.com/downloads/default.asp?url=/downloads/sample.asp?url=/msdn-files/027/001/766/msdncompositedoc.xml for details.
This column has only scratched the surface of XSLT. It's a complex but powerful programming language that, once you learn how to use it, yields vast gains in productivity that spring from the original promise of XML - separating content from presentation.
In his session at @ThingsExpo, Eric Lachapelle, CEO of the Professional Evaluation and Certification Board (PECB), will provide an overview of various initiatives to certifiy the security of connected devices and future trends in ensuring public trust of IoT. Eric Lachapelle is the Chief Executive Officer of the Professional Evaluation and Certification Board (PECB), an international certification body. His role is to help companies and individuals to achieve professional, accredited and worldw...
Mar. 24, 2017 08:15 PM EDT Reads: 244
DevOps is often described as a combination of technology and culture. Without both, DevOps isn't complete. However, applying the culture to outdated technology is a recipe for disaster; as response times grow and connections between teams are delayed by technology, the culture will die. A Nutanix Enterprise Cloud has many benefits that provide the needed base for a true DevOps paradigm.
Mar. 24, 2017 08:00 PM EDT Reads: 1,502
Your homes and cars can be automated and self-serviced. Why can't your storage? From simply asking questions to analyze and troubleshoot your infrastructure, to provisioning storage with snapshots, recovery and replication, your wildest sci-fi dream has come true. In his session at @DevOpsSummit at 20th Cloud Expo, Dan Florea, Director of Product Management at Tintri, will provide a ChatOps demo where you can talk to your storage and manage it from anywhere, through Slack and similar services ...
Mar. 24, 2017 06:30 PM EDT Reads: 4,105
My team embarked on building a data lake for our sales and marketing data to better understand customer journeys. This required building a hybrid data pipeline to connect our cloud CRM with the new Hadoop Data Lake. One challenge is that IT was not in a position to provide support until we proved value and marketing did not have the experience, so we embarked on the journey ourselves within the product marketing team for our line of business within Progress. In his session at @BigDataExpo, Sum...
Mar. 24, 2017 06:30 PM EDT Reads: 2,604
What sort of WebRTC based applications can we expect to see over the next year and beyond? One way to predict development trends is to see what sorts of applications startups are building. In his session at @ThingsExpo, Arin Sime, founder of WebRTC.ventures, will discuss the current and likely future trends in WebRTC application development based on real requests for custom applications from real customers, as well as other public sources of information,
Mar. 24, 2017 05:30 PM EDT Reads: 373
SYS-CON Events announced today that SoftLayer, an IBM Company, has been named “Gold Sponsor” of SYS-CON's 18th Cloud Expo, which will take place on June 7-9, 2016, at the Javits Center in New York, New York. SoftLayer, an IBM Company, provides cloud infrastructure as a service from a growing number of data centers and network points of presence around the world. SoftLayer’s customers range from Web startups to global enterprises.
Mar. 24, 2017 05:15 PM EDT Reads: 1,290
SYS-CON Events announced today that Ocean9will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Ocean9 provides cloud services for Backup, Disaster Recovery (DRaaS) and instant Innovation, and redefines enterprise infrastructure with its cloud native subscription offerings for mission critical SAP workloads.
Mar. 24, 2017 04:45 PM EDT Reads: 1,765
SYS-CON Events announced today that Linux Academy, the foremost online Linux and cloud training platform and community, will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Linux Academy was founded on the belief that providing high-quality, in-depth training should be available at an affordable price. Industry leaders in quality training, provided services, and student certification passes, its goal is to c...
Mar. 24, 2017 01:15 PM EDT Reads: 3,844
SYS-CON Events announced today that Interoute, owner-operator of one of Europe's largest networks and a global cloud services platform, has been named “Bronze Sponsor” of SYS-CON's 20th Cloud Expo, which will take place on June 6-8, 2017 at the Javits Center in New York, New York. Interoute is the owner-operator of one of Europe's largest networks and a global cloud services platform which encompasses 12 data centers, 14 virtual data centers and 31 colocation centers, with connections to 195 add...
Mar. 24, 2017 01:15 PM EDT Reads: 562
SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 20th International Cloud Expo, which will take place on June 6–8, 2017, at the Javits Center in New York City, NY. Telecom Reseller reports on Unified Communications, UCaaS, BPaaS for enterprise and SMBs. They report extensively on both customer premises based solutions such as IP-PBX as well as cloud based and hosted platforms.
Mar. 24, 2017 12:45 PM EDT Reads: 1,859
SYS-CON Events announced today that Loom Systems will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Founded in 2015, Loom Systems delivers an advanced AI solution to predict and prevent problems in the digital business. Loom stands alone in the industry as an AI analysis platform requiring no prior math knowledge from operators, leveraging the existing staff to succeed in the digital era. With offices in S...
Mar. 24, 2017 12:15 PM EDT Reads: 958
Keeping pace with advancements in software delivery processes and tooling is taxing even for the most proficient organizations. Point tools, platforms, open source and the increasing adoption of private and public cloud services requires strong engineering rigor - all in the face of developer demands to use the tools of choice. As Agile has settled in as a mainstream practice, now DevOps has emerged as the next wave to improve software delivery speed and output. To make DevOps work, organization...
Mar. 24, 2017 12:15 PM EDT Reads: 1,396
SYS-CON Events announced today that T-Mobile will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. As America's Un-carrier, T-Mobile US, Inc., is redefining the way consumers and businesses buy wireless services through leading product and service innovation. The Company's advanced nationwide 4G LTE network delivers outstanding wireless experiences to 67.4 million customers who are unwilling to compromise on ...
Mar. 24, 2017 12:00 PM EDT Reads: 1,886
SYS-CON Events announced today that Cloudistics, an on-premises cloud computing company, has been named “Bronze Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Cloudistics delivers a complete public cloud experience with composable on-premises infrastructures to medium and large enterprises. Its software-defined technology natively converges network, storage, compute, virtualization, and management into a ...
Mar. 24, 2017 12:00 PM EDT Reads: 1,640
SYS-CON Events announced today that CA Technologies has been named “Platinum Sponsor” of SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY, and the 21st International Cloud Expo®, which will take place October 31-November 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. CA Technologies helps customers succeed in a future where every business – from apparel to energy – is being rewritten by software. From ...
Mar. 24, 2017 10:45 AM EDT Reads: 1,421
SYS-CON Events announced today that Infranics will exhibit at SYS-CON's 20th International Cloud Expo®, which will take place on June 6-8, 2017, at the Javits Center in New York City, NY. Since 2000, Infranics has developed SysMaster Suite, which is required for the stable and efficient management of ICT infrastructure. The ICT management solution developed and provided by Infranics continues to add intelligence to the ICT infrastructure through the IMC (Infra Management Cycle) based on mathemat...
Mar. 24, 2017 09:45 AM EDT Reads: 2,736
Now that the world has connected “things,” we need to build these devices as truly intelligent in order to create instantaneous and precise results. This means you have to do as much of the processing at the point of entry as you can: at the edge. The killer use cases for IoT are becoming manifest through AI engines on edge devices. An autonomous car has this dual edge/cloud analytics model, producing precise, real-time results. In his session at @ThingsExpo, John Crupi, Vice President and Eng...
Mar. 24, 2017 08:45 AM EDT Reads: 3,679
In the enterprise today, connected IoT devices are everywhere – both inside and outside corporate environments. The need to identify, manage, control and secure a quickly growing web of connections and outside devices is making the already challenging task of security even more important, and onerous. In his session at @ThingsExpo, Rich Boyer, CISO and Chief Architect for Security at NTT i3, will discuss new ways of thinking and the approaches needed to address the emerging challenges of securit...
Mar. 24, 2017 08:30 AM EDT Reads: 4,263
The taxi industry never saw Uber coming. Startups are a threat to incumbents like never before, and a major enabler for startups is that they are instantly “cloud ready.” If innovation moves at the pace of IT, then your company is in trouble. Why? Because your data center will not keep up with frenetic pace AWS, Microsoft and Google are rolling out new capabilities In his session at 20th Cloud Expo, Don Browning, VP of Cloud Architecture at Turner, will posit that disruption is inevitable for c...
Mar. 24, 2017 08:30 AM EDT Reads: 1,907
There are 66 million network cameras capturing terabytes of data. How did factories in Japan improve physical security at the facilities and improve employee productivity? Edge Computing reduces possible kilobytes of data collected per second to only a few kilobytes of data transmitted to the public cloud every day. Data is aggregated and analyzed close to sensors so only intelligent results need to be transmitted to the cloud. Non-essential data is recycled to optimize storage.
Mar. 24, 2017 08:15 AM EDT Reads: 2,903