Welcome!

Industrial IoT Authors: XebiaLabs Blog, Elizabeth White, Antonella Corno, Liz McMillan, Jyoti Bansal

Related Topics: Industrial IoT

Industrial IoT: Article

An Introduction to XSLT

An Introduction to XSLT

You've probably heard the propaganda by now: XML blesses you with a way to separate content from presentation. Separation in turn yields productive gains over HTML and other data formats used to manage content.

In a process sometimes called single sourcing, the content of an XML document can be formatted for display in a Web browser, reformatted for delivery to such devices as mobile phones and handheld computers, and converted into a PDF file suitable for printing.

A news story, for example, that has been marked up in XML can be transformed into HTML for publication on a Web site, converted into Wireless Markup Language (WML) for display on a cell phone's screen, and rendered into a format from which a PDF file can be generated. Meantime, parts of the news story, such as paragraphs that supply background information about a given subject, can be reused in other XML-encoded news stories. What makes all this possible? XSLT.

Extensible Stylesheet Language for Transformations, or XSLT, is a functional programming language that enables us to bridge the gap between content and presentation by providing a means of specifying how a content-based XML document is transformed into a presentation-oriented document or data format.

This tutorial, written primarily for content authors, technical writers, Web designers, and other nonprogrammers, is the first in a short series that aims to introduce you to the basics of XSLT and help you get started using it to transform XML documents into HTML. The focus is not on data-centric documents but on such narrative-centric documents as reference manuals, help files, essays, stories, instructions, books, and magazine articles.

I'll begin by briefly summarizing the background of XSL and contrasting XSLT with XSL-FO and Cascading Style Sheets (CSS). Along the way I'll discuss what XSLT is, what it can do, and how to use it in conjunction with CSS to separate content from presentation. The next section will introduce you to XSLT's most fundamental component, the template rule, and demonstrate how to write one, culminating in a simple XSLT stylesheet that uses Internet Explorer 5.5's XSLT processor to transform a simple XML document into an HTML document.

XSLT, XSL-FO, and CSS
The birth of XSLT breaks down like this: Extensible Stylesheet Language, or XSL, was conceived as an XML application for expressing stylesheets capable of manipulating XML documents. After its submission to the W3C in 1997, XSL split into two stylesheet standards: Extensible Stylesheet Language for Transformations (XSLT) and Extensible Stylesheet Language Formatting Objects (XSL-FO).

XSLT is a language for transforming XML documents into typically other XML documents, HTML, and WML, but can also be used to produce documents in plain text and XSL-FO.

XSL-FO is used to describe the layout of XML documents for printing, with the end product usually being in Portable Document Format (PDF). XSL-FO, a complex standard that some refer to simply as XSL, may eventually also be employed to lay out Web pages, though this use is unsupported by current versions of Web browsers. You can find more information about XSLT and XSL-FO, including their specifications, on the World Wide Web Consortium's Web site, www.w3c.org. This column focuses on XSLT; later tutorials will expand on XSLT and delve into XSL-FO.

The early XSL proposals also gave rise to another breakaway standard, XPath. It grew out of the location-finding aspects of the XSL and XPointer specifications, which had been independently using similar mechanisms to find information in XML documents. XSLT uses XPath heavily to locate specific nodes or node sets within XML documents. Details about XPath can be found at www.w3c.org/TR/xpath

XSL has another related standard, though, unlike XSL, it isn't based on XML: Cascading Style Sheets. In the context of Web publishing, CSS can also be used, at least theoretically, to statically format XML documents for display, but it can't be used to transform them in any meaningful way. For example, XMetal, a tool for writing and editing in XML, uses CSS to format XML documents for display in its normal view. But until there is much stronger Web browser support for displaying XML documents with CSS, it isn't a practical option for Web publishing.

CSS isn't a competitor of XSLT. It's a method for statically formatting an XML document in a way that allows you to separate formatting and styling information from the document, but it doesn't allow you to dynamically transform an XML document into another data format. With CSS you can't manipulate the structure of an XML document, change the ordering of content, or dynamically generate a table of contents from a set of headings. Only XSLT can do that.

Using CSS to complement XSLT, however, is a powerful strategy for building Web pages - a strategy that splits presentation into what I call formatting and styling. Formatting can 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. Although the distinction between the two is not always clear-cut, formatting typically appears in the form of elements, styling information in the form of attribute-value pairs. For example, in <h1 style="color: olive;"> the h1 element formats the text as a first-level heading while the values of the style attribute, used for specifying inline CSS styles, reflect how the text should be styled.

You can gain a great deal of utility from separating as much styling information as possible from the formatting and placing it in a Cascading Style Sheet, although until the second major version of CSS (CSS Level 2) is better supported by browsers, your HTML formatting markup will still have to retain some styling information, such as that for tables.

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 changes in one file, the Cascading Style Sheet. Cascading Style Sheets: The Definitive Guide, published by O'Reilly, provides a detailed account of how to use CSS. The W3C CSS specifications are available at www.w3c.org/Style/CSS/. In this tutorial, I'll begin demonstrating how to use CSS with XSLT to separate styling from formatting, and I'll expand on the topic in later tutorials.

Preliminaries: Principles of Separation
Other principles of separation can be immensely useful in building well-engineered, text-based Web pages with XML, XSLT, CSS, and HTML. An overarching objective is to use XML to structure content and XSLT and CSS to format it in a way that minimizes redundancy and maximizes flexibility, including the capability to repurpose content and publish it in various formats. Most of the principles that follow are best applied to narrative-oriented documents that will be published as white papers, technical manuals, help files, essays, and so forth. Keep in mind that these principles are merely a guide and that the list of exceptions is long: your data, purpose, audience, delivery format, and other factors will influence how you engineer your system's own matrix of structure, metainformation, parameters, content, and presentation.

  • XML documents: Strive to maximize the content that exists as text, not as tags, in your XML documents. In other words, content that you expect end users to see should usually be set as content, not as elements or attributes. Avoid setting content as tags, either as elements or attributes, even if doing so comes at the cost of some redundancy; it's easier for content authors to work with content that is out in the open, not hidden as the value of attributes or as elements themselves. Instead, use elements to describe the structure or content of your material; use attributes to capture metainformation about the content or its structure and to encode parameters that are used to process the content. Place recurring content, especially content that may change, such as the name of a product under development, in entities. Shy away from placing formatting or styling information in your XML documents, although it may be expedient to include some table- and image-formatting instructions.
  • XSLT stylesheets: Place as much formatting information as possible in your XSLT stylesheet and eschew using it as a container for standard content. Instead, place content out in the open in your XML documents even if doing so comes at the expense of a little duplication. However, highly variable content, such as the date of publication and the version number, may be best placed in the XSLT stylesheet as entities. It may also benefit you to make exceptions for content that varies by audience, as in the case of parameterized settings used in internationalization.
  • Cascading Style Sheets: As I mentioned above, these should complement the XSLT stylesheet by containing as many as possible of the formatting code's visual styling properties.

    In the examples that accompany this and later tutorials in the series, you'll see some of these principles at work.

XSLT's Atom: 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. (Actually, it's the XSLT processor that takes an XML document, called a source tree, and an XSLT stylesheet as input and uses them to produce a result tree as output, which can then be serialized into a file, but we don't need to worry about such technicalities just yet.) A template rule is an XSL element that matches a node in the XML source document and typically applies an output format to it. For example, say you have the following simple XML document:

<?xml version="1.0"?>
<source>
<message>Greetings and
Salutations.</message>
</source>

You can use a template rule to find the children of the <source> element and to format its contents in HTML for presentation. Here's an XSLT template rule that does just that:

<xsl:template match="/">
<html>
<body>
<h1><xsl:apply- templates/></h1> </body>
</html>
</xsl:template>

In the above 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="source">. 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.

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 <source> node in our XML file, <xsl:apply-templates> suffices to print the meager contents of the file. If, however, the <source> 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 processed and outputted.

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:

  1. We need to add an XML processing instruction to the top of the stylesheet.
  2. 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/" for details):
<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl=
"http://www.w3.org/1999/XSL/
Transform"
version="1.0">
<xsl:template match="/">
<html>
<body>
<h1><xsl:apply- templates/ ></h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

We now have a minimal stylesheet that will convert our XML source to HTML. To view the output in IE 5.5 or greater, 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, which in this case is located in the same directory as the source file, as the path in the href attribute's value testifies:

<?xml version="1.0"?>
<?xml:stylesheet type="text/xsl"
href="my_stylesheet.xsl"?>
<source>
<message>Greetings and Salutations.</message>
</source>

Let's expand our minimal stylesheet to do a few more things. First, we'll modify our template rule to output the message element specifically (as opposed to all the children of the root element); second, we'll add a link to a CSS that specifies the visual properties of our HTML formatting:

<?xml version="1.0"?>
<xsl:stylesheet xmlns:xsl= "http://www.w3.org/1999/XSL/Transform" version="1.0" >
<xsl:template match="source">
<html>
<head>
<link rel= "stylesheet"type= "text/css" href= "my_styles.css"/>
</head>
<body>
<h1><xsl:value- of select= "message"/></h1>
</body>
</html>
</xsl:template>
</xsl:stylesheet>

This stylesheet first matches the root node explicitly by name (source), 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.

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 following code:

h1 { color: olive; }
This simple code selects the <h1> element and renders it in olive in Internet Explorer, effectively separating the color aspect of the heading's visual style from its HTML formatting code in the XSLT stylesheet.

Because XSLT is a programming language, there's a great deal more to it than the simple examples shown above. To reinforce this column's brief introduction, I suggest you read Chapter 6, "Transformation: Repurposing Documents," in O'Reilly's Learning XML. 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 creating an XML document and write some simple template matching rules like those above to process your source and output it in Internet Explorer. My next column will delve deeper into XSLT to unearth its complexity and accompanying power.

More Stories By Steve Hoenisch

Steve Hoenisch is a technical writer (consultant) with Verizon
Wireless. Before becoming a technical writer and a Web developer, he
worked as a journalist and teacher. Steve has been developing Web
sites since 1996.

Comments (2) View Comments

Share your thoughts on this story.

Add your comment
You must be signed in to add a comment. Sign-in | Register

In accordance with our Comment Policy, we encourage comments that are on topic, relevant and to-the-point. We will remove comments that include profanity, personal attacks, racial slurs, threats of violence, or other inappropriate material that violates our Terms and Conditions, and will block users who make repeated violations. We ask all readers to expect diversity of opinion and to treat one another with dignity and respect.


Most Recent Comments
Robert Klawuhn 01/21/02 02:34:00 PM EST

Steve,

I am trying to make your examples work with my IE 5.5 browser. When I look at msdn.microsoft.com, I see the same namespace, so I left it alone in the files below.

I created the three files, my_xml.xml, my_stylesheet.xsl, and my_styles.css using the code from your article.

When I double-click my_xml.xml, my IE 5.5 just shows the xml. There doesn't seem to be any interaction with the xsl or css files. Is this how to launch the formatted xml?

I am very new to XML and XSL. Can you
give me any hints as to how to make this work?

Thanks,
Bob

*** my_xml.xml ***

Greetings and Salutations.

*** my_stylesheet.xsl ***

HI THERE

*** my_styles.css ***
h1 { color: olive; }

Jan Semmelink 01/21/02 03:41:00 AM EST

Your subheader reads "Using sylesheets to seperate..." instead of "Using stylesheets..." (missing "t").

@ThingsExpo Stories
Bert Loomis was a visionary. This general session will highlight how Bert Loomis and people like him inspire us to build great things with small inventions. In their general session at 19th Cloud Expo, Harold Hannon, Architect at IBM Bluemix, and Michael O'Neill, Strategic Business Development at Nvidia, discussed the accelerating pace of AI development and how IBM Cloud and NVIDIA are partnering to bring AI capabilities to "every day," on-demand. They also reviewed two "free infrastructure" pr...
In his keynote at @ThingsExpo, Chris Matthieu, Director of IoT Engineering at Citrix and co-founder and CTO of Octoblu, focused on building an IoT platform and company. He provided a behind-the-scenes look at Octoblu’s platform, business, and pivots along the way (including the Citrix acquisition of Octoblu).
Data is an unusual currency; it is not restricted by the same transactional limitations as money or people. In fact, the more that you leverage your data across multiple business use cases, the more valuable it becomes to the organization. And the same can be said about the organization’s analytics. In his session at 19th Cloud Expo, Bill Schmarzo, CTO for the Big Data Practice at Dell EMC, introduced a methodology for capturing, enriching and sharing data (and analytics) across the organization...
The explosion of new web/cloud/IoT-based applications and the data they generate are transforming our world right before our eyes. In this rush to adopt these new technologies, organizations are often ignoring fundamental questions concerning who owns the data and failing to ask for permission to conduct invasive surveillance of their customers. Organizations that are not transparent about how their systems gather data telemetry without offering shared data ownership risk product rejection, regu...
Grape Up is a software company, specialized in cloud native application development and professional services related to Cloud Foundry PaaS. With five expert teams that operate in various sectors of the market across the USA and Europe, we work with a variety of customers from emerging startups to Fortune 1000 companies.
Financial Technology has become a topic of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 20th Cloud Expo at the Javits Center in New York, June 6-8, 2017, will find fresh new content in a new track called FinTech.
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...
Multiple data types are pouring into IoT deployments. Data is coming in small packages as well as enormous files and data streams of many sizes. Widespread use of mobile devices adds to the total. In this power panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists will look at the tools and environments that are being put to use in IoT deployments, as well as the team skills a modern enterprise IT shop needs to keep things running, get a handle on all this data, and deli...
The age of Digital Disruption is evolving into the next era – Digital Cohesion, an age in which applications securely self-assemble and deliver predictive services that continuously adapt to user behavior. Information from devices, sensors and applications around us will drive services seamlessly across mobile and fixed devices/infrastructure. This evolution is happening now in software defined services and secure networking. Four key drivers – Performance, Economics, Interoperability and Trust ...
The Internet of Things is clearly many things: data collection and analytics, wearables, Smart Grids and Smart Cities, the Industrial Internet, and more. Cool platforms like Arduino, Raspberry Pi, Intel's Galileo and Edison, and a diverse world of sensors are making the IoT a great toy box for developers in all these areas. In this Power Panel at @ThingsExpo, moderated by Conference Chair Roger Strukhoff, panelists discussed what things are the most important, which will have the most profound e...
@ThingsExpo has been named the Most Influential ‘Smart Cities - IIoT' Account and @BigDataExpo has been named fourteenth by Right Relevance (RR), which provides curated information and intelligence on approximately 50,000 topics. In addition, Right Relevance provides an Insights offering that combines the above Topics and Influencers information with real time conversations to provide actionable intelligence with visualizations to enable decision making. The Insights service is applicable to eve...
SYS-CON Events announced today that Grape Up will exhibit at SYS-CON's 21st International Cloud Expo®, which will take place on Oct. 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA. Grape Up is a software company specializing in cloud native application development and professional services related to Cloud Foundry PaaS. With five expert teams that operate in various sectors of the market across the U.S. and Europe, Grape Up works with a variety of customers from emergi...
SYS-CON Events announced today that Hitachi, the leading provider the Internet of Things and Digital Transformation, 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. Hitachi Data Systems, a wholly owned subsidiary of Hitachi, Ltd., offers an integrated portfolio of services and solutions that enable digital transformation through enhanced data management, governance, mobility and analytics. We help globa...
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.
20th Cloud Expo, taking place June 6-8, 2017, at the Javits Center in New York City, NY, will feature technical sessions from a rock star conference faculty and the leading industry players in the world. Cloud computing is now being embraced by a majority of enterprises of all sizes. Yesterday's debate about public vs. private has transformed into the reality of hybrid cloud: a recent survey shows that 74% of enterprises have a hybrid cloud strategy.
SYS-CON Events announced today that Super Micro Computer, Inc., a global leader in compute, storage and networking technologies, 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. Supermicro (NASDAQ: SMCI), the leading innovator in high-performance, high-efficiency server technology, is a premier provider of advanced server Building Block Solutions® for Data Center, Cloud Computing, Enterprise IT, Hadoop/...
Amazon has gradually rolled out parts of its IoT offerings in the last year, but these are just the tip of the iceberg. In addition to optimizing their back-end AWS offerings, Amazon is laying the ground work to be a major force in IoT – especially in the connected home and office. Amazon is extending its reach by building on its dominant Cloud IoT platform, its Dash Button strategy, recently announced Replenishment Services, the Echo/Alexa voice recognition control platform, the 6-7 strategic...
Judith Hurwitz is president and CEO of Hurwitz & Associates, a Needham, Mass., research and consulting firm focused on emerging technology, including big data, cognitive computing and governance. She is co-author of the book Cognitive Computing and Big Data Analytics, published in 2015. Her Cloud Expo session, "What Is the Business Imperative for Cognitive Computing?" is scheduled for Wednesday, June 8, at 8:40 a.m. In it, she puts cognitive computing into perspective with its value to the busin...
Cognitive Computing is becoming the foundation for a new generation of solutions that have the potential to transform business. Unlike traditional approaches to building solutions, a cognitive computing approach allows the data to help determine the way applications are designed. This contrasts with conventional software development that begins with defining logic based on the current way a business operates. In her session at 18th Cloud Expo, Judith S. Hurwitz, President and CEO of Hurwitz & ...
Cybersecurity is a critical component of software development in many industries including medical devices. However, code is not always written to be robust or secure from the unknown or the unexpected. This gap can make medical devices susceptible to cybersecurity attacks ranging from compromised personal health information to life-sustaining treatment. In his session at @ThingsExpo, Clark Fortney, Software Engineer at Battelle, will discuss how programming oversight using key methods can incre...