Click here to close now.

Welcome!

XML Authors: Navrup Johal, AppDynamics Blog, Jayaram Krishnaswamy, Cloud Best Practices Network, Jnan Dash

Related Topics: XML

XML: Article

Modularize Formatting Objects

Modularize Formatting Objects

The Extensible Stylesheet Language (XSL) W3C recommendation was created as a means to display XML data. The recommendation includes a transformation language (XSLT) and formatting object (or output format) language (XSL-FO), which together provide the XSL stylesheet developer with the tools necessary to present XML.

The XSL-FO language is like HTML on steroids, because it allows not only cascading stylesheet (CSS)-type functionality, but also pagination and page layout, which are not available using HTML alone (at least not to as great a degree as with XSL-FO). However, such robustness comes at a cost; the language is very (very) verbose, which makes writing XSL-FO XSL stylesheets very difficult; thus, XSL-FO stylesheets are supposed to be produced as the result of an XSL transformation. But someone has to write the XSL stylesheet that transforms the XML into XSL-FO, and that's where this article can help.

The purpose of this article is to show you, the XSL stylesheet developer, how to make XSL-FO XSL stylesheets that are flexible and reusable. In other words, I'm going to show you how to make modularized XSL-FO XSL stylesheets.

Many of the key concepts presented in this article are not XSL-FO specific and can be leveraged to write any kind of XSL stylesheet. However, I concentrated on XSL-FO XSL stylesheets because their verbosity highlights the need for modularization more than most stylesheets.

I'm assuming a working knowledge of both XSLT and XSL-FO. For an introduction, you can refer to many resources on the Internet, including my article in the January 2002 edition of XML-Journal.

Overview of the Solution
Although this modularization solution is very flexible, it is also very simple and uses the XSL <xsl:import> and <xsl:attribute-set> elements, along with the xsl:use-attribute-sets attribute. When used properly, these elements and this attribute not only allow you to externalize the way an XML document is transformed into an XSL-FO document (<xsl:import>), but also the look-and-feel of the eventual FO document (<xsl:attribute-set>, xsl:use-attribute-sets). Figure 1 depicts all the pieces of these concepts.

From a high level, the XSLT engine reads in an XML document and XSL stylesheet (nothing new there). The main stylesheet, the one that is read by the XSLT engine, then uses <xsl:import> to use two additional stylesheets - one for the layout of the XSL-FO document and another for the "look-and-feel." The layout document then uses the use-attribute-sets attribute to get the "look-and-feel" (i.e., element attribution information) data from the "look-and-feel" XSL stylesheet, which is implemented as a series of <xsl:attribute-set> elements.

With the layout and look-and-feel externalized and separated into different stylesheets, the stylesheet writer can easily exchange both/either the layout and/or look-and-feel of the XSL-FO document information. If the XSL-FO document has such flexibility, it follows that the layout and look-and-feel of the eventual output document, a PDF file for example, has equal flexibility.

A Presentation Example
The example I'm going to present is a good case for the advantages of using a modular design in XSL. In presentation graphics (e.g., Microsoft PowerPoint), there are templates that can change the layout of pages and the color/graphics scheme of your presentation. I am going to replicate, to some degree, that same kind of functionality using XSL. If you use the ideas in this example, you can impress your friends by creating PDF presentations that are cross-platform with data separated from the presentation (which implies that the same data could potentially be used in entirely different formats).

The XML file
The data for the sample is represented in a simple XML file, named presentation.xml, that depicts the idea of a presentation with pages containing concepts (such a format is probably a little too coupled to the presentation, but it'll work). The root element of the document is "Presentation," with descriptive child elements called "Title," "Author," "Date," and "CorporateLogo," and a series of "Page" elements that take the following form:

<Page style="bullet">
<Position>01</Position>
<Title>Title Text</Title>
<Concept>Some concept</Concept>
...more concepts
</Page>

The "style" attribute is referred to in the layout stylesheet to create the proper text layout in the presentation (e.g, PDF) output. The example is bullet, but you could extend the idea to be graphic, column, bullet-graphic, or any other style you require. You'll see shortly how the value of this attribute is used.

The position element allows you to put the "Page" elements in any order within the XML document and still have them laid out the way you want in the final output. Like the "style" attribute, the "Position" element is used by the layout stylesheet.

The main XSL stylesheet
Ultimately, the XSLT engine requires the name of a stylesheet to be processed. In this example, that file is called main.xsl and is very simple since its main purpose is to point to the correct layout and look-and-feel stylesheet. Listing 1 shows the contents of that stylesheet, minus the XML declaration and <xsl:stylesheet> element.

Within Listing 1, the <xsl:import> elements point to the layout and look-and-feel stylesheet, respectively. To change the template, you simply create a new layout and/or look-and-feel stylesheet and change the value of the import.

The other interesting point of the main.xsl stylesheet is simply that it creates the <fo:root> element and uses the <xsl:apply-templates> to transfer processing to other templates (which are defined in the plainPageLayout.xsl stylesheet).

Look-and-feel
The lookandfeel.xsl stylesheet contains a number of <xsl:attribute-set> definitions, which can be referenced using the xsl:use-attribute-sets property with an FO element. The contents of each <xsl:attribute-set> are the equivalent of attributes on XSL elements.

Take, for instance, a relatively simple <fo:simple-page-master> element, which defines a template for a page.

<fo:simple-page-master
master-name="Title"
margin-top="1in"
margin-bottom="1in"
margin-left="1in"
margin-right="1in"
page-height="8.5in"
page-width="11in"
>

<fo:region-body/>
<fo:region-after
extent="1in"/>
</fo:simple-page-master>

You can externalize all the attributes of the <fo:simple-page-master> element into the lookandfeel.xsl file by defining an <xsl:attribute-set> element as follows:

<xsl:attribute-set name="titlePage
Layout">
<xsl:attribute name="margin-
top">3in</xsl:attribute>
<xsl:attribute name="margin-
bottom">1in</xsl:attribute>
<xsl:attribute name="margin-
left">1in</xsl:attribute>
<xsl:attribute name="margin-
right">1in</xsl:attribute>
<xsl:attribute name="page-
height">8.5in</xsl:attribute>
<xsl:attribute name="page-
width">11in</xsl:attribute>
</xsl:attribute-set>

Then, you can refer to the attribute set within the <fo:simple-page-master> by using the "xsl:use-attribute-sets" attribute, such as:

<fo:simple-page-master
master-name="Title"
xsl:use-attribute-sets="titlePageLayout">

Not only is the syntax easier to read, but the attributes values themselves are now externalized from the layout in what's essentially the FO equivalent of an external CSS.

Page layout
In XSL-FO, layout is a matter of setting up page definitions and their contents. In my example, I use the page layout XSL document, named plainPageLayout.xsl, to perform the template matching on the XML document contents. I did this because the layout is responsible for understanding the output document, something that requires knowledge of the XML input, since the data from the latter becomes part of the former.

The plainPageLayout.xsl document itself looks like most XSL-FO stylesheets. However, instead of very long attribute listings (for look-and-feel type attributes), there are several xsl:use-attribute-sets attributes.

In terms of XSLT, plainPageLayout. xsl contains three templates: one each to process the "Presentation," "Page," and "Concept" elements, respectively. That presentation template creates the basic layout of the resulting XSL-FO document and then creates the title page, using data from the XML document. Throughout this stylesheet, xsl:use-attribute-sets attributes are used within <fo> elements to retrieve attributes from lookandfeel.xsl.

The Page template actually processes Page elements by style. That is, the

<xsl:template match="Page[@style='bullet']">

element will catch the "bullet" style pages only. Within the template, the non-title pages are set up with a title and two blank lines, after which the "Concept" elements are selected within a <xsl:apply templates select="Concept"/> statement. Finally, the "Concept" template processes each "Concept," creating an XSL-FO list with bullets.

As a side note, the stylesheet can be made even more modularized if you were to externalize your "Page" and/or "Concept" templates. Doing so would let you use the "bullet" style across different layout XSL documents. I did not do so for the sake of simplicity.

Listing 2 shows the entire contents of plainPageLayout.xsl. Within Listing 2, notice the comment that reads "<!-- Shows how to override attributes. -->." What I'm showing at that point in the stylesheet is that even if an XSL-FO element uses an attribute set, you can still override and/or amend the attribute set within the element itself, much in the same way you can override/add to an HTML element if a CSS is defined - further evidence of the CSS-like nature of attribute sets.

The result
I believe that the proof of any technology is in the pudding. When you run presentation.xml and main.xsl through an FO processor (I used FOP 0.20.3), you will end up with a three-page PDF (if you choose the PDF output option within FOP). Figures 2 and 3 show the first two pages. Page 3 is just like page 2 but contains different concepts (refer to presentation.xml).

Figure 2 shows not only the main "Presentation" element (and the relevant non-page children of "Presentation"), but it also shows some of the XSL-FO design I created. For instance, the logo and yellow background color. The color and font characteristics are externalized within lookandfeel.xsl, of course.

Figure 3 uses the same basic layout characteristics of the title page, but also contains the list of concepts. Every "Page" that uses the "bullet" style will be rendered just as Figure 3 (refer to the third page of presentation.pdf if you download the source code, available at www.sys-con.com/xml/sourcec.cfm).

Conclusion
XSL-FO XSL stylesheets are long and difficult to read and write. Furthermore, it's not easy to change layout and look-and-feel without additional modularization. Using the XSL <xsl:import> and <xsl:attribute-sets> elements along with the xsl:use-attribute-sets attribute can go a very long way toward making such modularization a reality.

Resources

  • XSL: www.w3.org/Style/XSL
  • Neugebauer, Frank. "XSL Formatting Objects: Here Today, Huge Tomorrow." (2002). XML-Journal. January: www.sys-con.com/xml/article.cfm?id=324
  • More Stories By Frank Neugebauer

    Frank Neugebauer is a consultant with the Insurance Solutions Group of IBM Global Services. He has been using Java since 1996 and has worked on the architecture and implementation of enterprise Java solutions using Servlets, EJBs, XML, and XSLT. He has also taught Java, HTML, and JavaScript at the University of Michigan Center for Corporate and Professional Development.

    Comments (0)

    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.


    @ThingsExpo Stories
    “In the past year we've seen a lot of stabilization of WebRTC. You can now use it in production with a far greater degree of certainty. A lot of the real developments in the past year have been in things like the data channel, which will enable a whole new type of application," explained Peter Dunkley, Technical Director at Acision, in this SYS-CON.tv interview at @ThingsExpo, held Nov 4–6, 2014, at the Santa Clara Convention Center in Santa Clara, CA.
    SYS-CON Events announced today that Ciqada will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Ciqada™ makes it easy to connect your products to the Internet. By integrating key components - hardware, servers, dashboards, and mobile apps - into an easy-to-use, configurable system, your products can quickly and securely join the internet of things. With remote monitoring, control, and alert messaging capability, you will meet your customers' needs of tomorrow - today! Ciqada. Let your products take flight. For more inform...
    Health care systems across the globe are under enormous strain, as facilities reach capacity and costs continue to rise. M2M and the Internet of Things have the potential to transform the industry through connected health solutions that can make care more efficient while reducing costs. In fact, Vodafone's annual M2M Barometer Report forecasts M2M applications rising to 57 percent in health care and life sciences by 2016. Lively is one of Vodafone's health care partners, whose solutions enable older adults to live independent lives while staying connected to loved ones. M2M will continue to gr...
    SYS-CON Media announced today that @WebRTCSummit Blog, the largest WebRTC resource in the world, has been launched. @WebRTCSummit Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @WebRTCSummit Blog can be bookmarked ▸ Here @WebRTCSummit conference site can be bookmarked ▸ Here
    SYS-CON Events announced today that GENBAND, a leading developer of real time communications software solutions, has been named “Silver Sponsor” of SYS-CON's WebRTC Summit, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. The GENBAND team will be on hand to demonstrate their newest product, Kandy. Kandy is a communications Platform-as-a-Service (PaaS) that enables companies to seamlessly integrate more human communications into their Web and mobile applications - creating more engaging experiences for their customers and boosting collaboration and productiv...
    Dave will share his insights on how Internet of Things for Enterprises are transforming and making more productive and efficient operations and maintenance (O&M) procedures in the cleantech industry and beyond. Speaker Bio: Dave Landa is chief operating officer of Cybozu Corp (kintone US). Based in the San Francisco Bay Area, Dave has been on the forefront of the Cloud revolution driving strategic business development on the executive teams of multiple leading Software as a Services (SaaS) application providers dating back to 2004. Cybozu's kintone.com is a leading global BYOA (Build Your O...
    The best mobile applications are augmented by dedicated servers, the Internet and Cloud services. Mobile developers should focus on one thing: writing the next socially disruptive viral app. Thanks to the cloud, they can focus on the overall solution, not the underlying plumbing. From iOS to Android and Windows, developers can leverage cloud services to create a common cross-platform backend to persist user settings, app data, broadcast notifications, run jobs, etc. This session provides a high level technical overview of many cloud services available to mobile app developers, includi...
    SYS-CON Events announced today that BroadSoft, the leading global provider of Unified Communications and Collaboration (UCC) services to operators worldwide, has been named “Gold Sponsor” of SYS-CON's WebRTC Summit, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. BroadSoft is the leading provider of software and services that enable mobile, fixed-line and cable service providers to offer Unified Communications over their Internet Protocol networks. The Company’s core communications platform enables the delivery of a range of enterprise and consumer calling...
    While not quite mainstream yet, WebRTC is starting to gain ground with Carriers, Enterprises and Independent Software Vendors (ISV’s) alike. WebRTC makes it easy for developers to add audio and video communications into their applications by using Web browsers as their platform. But like any market, every customer engagement has unique requirements, as well as constraints. And of course, one size does not fit all. In her session at WebRTC Summit, Dr. Natasha Tamaskar, Vice President, Head of Cloud and Mobile Strategy at GENBAND, will explore what is needed to take a real time communications ...
    What exactly is a cognitive application? In her session at 16th Cloud Expo, Ashley Hathaway, Product Manager at IBM Watson, will look at the services being offered by the IBM Watson Developer Cloud and what that means for developers and Big Data. She'll explore how IBM Watson and its partnerships will continue to grow and help define what it means to be a cognitive service, as well as take a look at the offerings on Bluemix. She will also check out how Watson and the Alchemy API team up to offer disruptive APIs to developers.
    The IoT Bootcamp is coming to Cloud Expo | @ThingsExpo on June 9-10 at the Javits Center in New York. Instructor. Registration is now available at http://iotbootcamp.sys-con.com/ Instructor Janakiram MSV previously taught the famously successful Multi-Cloud Bootcamp at Cloud Expo | @ThingsExpo in November in Santa Clara. Now he is expanding the focus to Janakiram is the founder and CTO of Get Cloud Ready Consulting, a niche Cloud Migration and Cloud Operations firm that recently got acquired by Aditi Technologies. He is a Microsoft Regional Director for Hyderabad, India, and one of the f...
    The 17th International Cloud Expo has announced that its Call for Papers is open. 17th International Cloud Expo, to be held November 3-5, 2015, at the Santa Clara Convention Center in Santa Clara, CA, brings together Cloud Computing, APM, APIs, Microservices, Security, Big Data, Internet of Things, DevOps and WebRTC to one location. With cloud computing driving a higher percentage of enterprise IT budgets every year, it becomes increasingly important to plant your flag in this fast-expanding business opportunity. Submit your speaking proposal today!
    WebRTC is an up-and-coming standard that enables real-time voice and video to be directly embedded into browsers making the browser a primary user interface for communications and collaboration. WebRTC runs in a number of browsers today and is currently supported in over a billion installed browsers globally, across a range of platform OS and devices. Today, organizations that choose to deploy WebRTC applications and use a host machine that supports audio through USB or Bluetooth can use Plantronics products to connect and transit or receive the audio associated with the WebRTC session.
    As enterprises move to all-IP networks and cloud-based applications, communications service providers (CSPs) – facing increased competition from over-the-top providers delivering content via the Internet and independently of CSPs – must be able to offer seamless cloud-based communication and collaboration solutions that can scale for small, midsize, and large enterprises, as well as public sector organizations, in order to keep and grow market share. The latest version of Oracle Communications Unified Communications Suite gives CSPs the capability to do just that. In addition, its integration ...
    SYS-CON Media announced today that @ThingsExpo Blog launched with 7,788 original stories. @ThingsExpo Blog offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. @ThingsExpo Blog can be bookmarked. The Internet of Things (IoT) is the most profound change in personal and enterprise IT since the creation of the Worldwide Web more than 20 years ago.
    The world's leading Cloud event, Cloud Expo has launched Microservices Journal on the SYS-CON.com portal, featuring over 19,000 original articles, news stories, features, and blog entries. DevOps Journal is focused on this critical enterprise IT topic in the world of cloud computing. Microservices Journal offers top articles, news stories, and blog posts from the world's well-known experts and guarantees better exposure for its authors than any other publication. Follow new article posts on Twitter at @MicroservicesE
    SYS-CON Events announced today that robomq.io will exhibit at SYS-CON's @ThingsExpo, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. robomq.io is an interoperable and composable platform that connects any device to any application. It helps systems integrators and the solution providers build new and innovative products and service for industries requiring monitoring or intelligence from devices and sensors.
    Wearable technology was dominant at this year’s International Consumer Electronics Show (CES) , and MWC was no exception to this trend. New versions of favorites, such as the Samsung Gear (three new products were released: the Gear 2, the Gear 2 Neo and the Gear Fit), shared the limelight with new wearables like Pebble Time Steel (the new premium version of the company’s previously released smartwatch) and the LG Watch Urbane. The most dramatic difference at MWC was an emphasis on presenting wearables as fashion accessories and moving away from the original clunky technology associated with t...
    SYS-CON Events announced today that Litmus Automation will exhibit at SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York City, NY. Litmus Automation’s vision is to provide a solution for companies that are in a rush to embrace the disruptive Internet of Things technology and leverage it for real business challenges. Litmus Automation simplifies the complexity of connected devices applications with Loop, a secure and scalable cloud platform.
    In 2015, 4.9 billion connected "things" will be in use. By 2020, Gartner forecasts this amount to be 25 billion, a 410 percent increase in just five years. How will businesses handle this rapid growth of data? Hadoop will continue to improve its technology to meet business demands, by enabling businesses to access/analyze data in real time, when and where they need it. Cloudera's Chief Technologist, Eli Collins, will discuss how Big Data is keeping up with today's data demands and how in the future, data and analytics will be pervasive, embedded into every workflow, application and infra...