Welcome!

Industrial IoT Authors: Elizabeth White, John Rauser, Liz McMillan, Pat Romanski, Madhavan Krishnan, VP, Cloud Solutions, Virtusa

Related Topics: Industrial IoT

Industrial IoT: 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
    Coca-Cola’s Google powered digital signage system lays the groundwork for a more valuable connection between Coke and its customers. Digital signs pair software with high-resolution displays so that a message can be changed instantly based on what the operator wants to communicate or sell. In their Day 3 Keynote at 21st Cloud Expo, Greg Chambers, Global Group Director, Digital Innovation, Coca-Cola, and Vidya Nagarajan, a Senior Product Manager at Google, discussed how from store operations and ...
    In his session at 21st Cloud Expo, Carl J. Levine, Senior Technical Evangelist for NS1, will objectively discuss how DNS is used to solve Digital Transformation challenges in large SaaS applications, CDNs, AdTech platforms, and other demanding use cases. Carl J. Levine is the Senior Technical Evangelist for NS1. A veteran of the Internet Infrastructure space, he has over a decade of experience with startups, networking protocols and Internet infrastructure, combined with the unique ability to it...
    "There's plenty of bandwidth out there but it's never in the right place. So what Cedexis does is uses data to work out the best pathways to get data from the origin to the person who wants to get it," explained Simon Jones, Evangelist and Head of Marketing at Cedexis, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
    SYS-CON Events announced today that CrowdReviews.com has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5–7, 2018, at the Javits Center in New York City, NY. CrowdReviews.com is a transparent online platform for determining which products and services are the best based on the opinion of the crowd. The crowd consists of Internet users that have experienced products and services first-hand and have an interest in letting other potential buye...
    "MobiDev is a software development company and we do complex, custom software development for everybody from entrepreneurs to large enterprises," explained Alan Winters, U.S. Head of Business Development at MobiDev, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
    SYS-CON Events announced today that Telecom Reseller has been named “Media Sponsor” of SYS-CON's 22nd International Cloud Expo, which will take place on June 5-7, 2018, at the Javits Center in New York, 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.
    WebRTC is great technology to build your own communication tools. It will be even more exciting experience it with advanced devices, such as a 360 Camera, 360 microphone, and a depth sensor camera. In his session at @ThingsExpo, Masashi Ganeko, a manager at INFOCOM Corporation, introduced two experimental projects from his team and what they learned from them. "Shotoku Tamago" uses the robot audition software HARK to track speakers in 360 video of a remote party. "Virtual Teleport" uses a multip...
    Gemini is Yahoo’s native and search advertising platform. To ensure the quality of a complex distributed system that spans multiple products and components and across various desktop websites and mobile app and web experiences – both Yahoo owned and operated and third-party syndication (supply), with complex interaction with more than a billion users and numerous advertisers globally (demand) – it becomes imperative to automate a set of end-to-end tests 24x7 to detect bugs and regression. In th...
    "Space Monkey by Vivent Smart Home is a product that is a distributed cloud-based edge storage network. Vivent Smart Home, our parent company, is a smart home provider that places a lot of hard drives across homes in North America," explained JT Olds, Director of Engineering, and Brandon Crowfeather, Product Manager, at Vivint Smart Home, in this SYS-CON.tv interview at @ThingsExpo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clara, CA.
    "IBM is really all in on blockchain. We take a look at sort of the history of blockchain ledger technologies. It started out with bitcoin, Ethereum, and IBM evaluated these particular blockchain technologies and found they were anonymous and permissionless and that many companies were looking for permissioned blockchain," stated René Bostic, Technical VP of the IBM Cloud Unit in North America, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Conventi...
    "Cloud Academy is an enterprise training platform for the cloud, specifically public clouds. We offer guided learning experiences on AWS, Azure, Google Cloud and all the surrounding methodologies and technologies that you need to know and your teams need to know in order to leverage the full benefits of the cloud," explained Alex Brower, VP of Marketing at Cloud Academy, in this SYS-CON.tv interview at 21st Cloud Expo, held Oct 31 – Nov 2, 2017, at the Santa Clara Convention Center in Santa Clar...
    It is of utmost importance for the future success of WebRTC to ensure that interoperability is operational between web browsers and any WebRTC-compliant client. To be guaranteed as operational and effective, interoperability must be tested extensively by establishing WebRTC data and media connections between different web browsers running on different devices and operating systems. In his session at WebRTC Summit at @ThingsExpo, Dr. Alex Gouaillard, CEO and Founder of CoSMo Software, presented ...
    A strange thing is happening along the way to the Internet of Things, namely far too many devices to work with and manage. It has become clear that we'll need much higher efficiency user experiences that can allow us to more easily and scalably work with the thousands of devices that will soon be in each of our lives. Enter the conversational interface revolution, combining bots we can literally talk with, gesture to, and even direct with our thoughts, with embedded artificial intelligence, whic...
    SYS-CON Events announced today that Evatronix 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. Evatronix SA offers comprehensive solutions in the design and implementation of electronic systems, in CAD / CAM deployment, and also is a designer and manufacturer of advanced 3D scanners for professional applications.
    Leading companies, from the Global Fortune 500 to the smallest companies, are adopting hybrid cloud as the path to business advantage. Hybrid cloud depends on cloud services and on-premises infrastructure working in unison. Successful implementations require new levels of data mobility, enabled by an automated and seamless flow across on-premises and cloud resources. In his general session at 21st Cloud Expo, Greg Tevis, an IBM Storage Software Technical Strategist and Customer Solution Architec...
    To get the most out of their data, successful companies are not focusing on queries and data lakes, they are actively integrating analytics into their operations with a data-first application development approach. Real-time adjustments to improve revenues, reduce costs, or mitigate risk rely on applications that minimize latency on a variety of data sources. In his session at @BigDataExpo, Jack Norris, Senior Vice President, Data and Applications at MapR Technologies, reviewed best practices to ...
    An increasing number of companies are creating products that combine data with analytical capabilities. Running interactive queries on Big Data requires complex architectures to store and query data effectively, typically involving data streams, an choosing efficient file format/database and multiple independent systems that are tied together through custom-engineered pipelines. In his session at @BigDataExpo at @ThingsExpo, Tomer Levi, a senior software engineer at Intel’s Advanced Analytics gr...
    When talking IoT we often focus on the devices, the sensors, the hardware itself. The new smart appliances, the new smart or self-driving cars (which are amalgamations of many ‘things’). When we are looking at the world of IoT, we should take a step back, look at the big picture. What value are these devices providing? IoT is not about the devices, it’s about the data consumed and generated. The devices are tools, mechanisms, conduits. In his session at Internet of Things at Cloud Expo | DXWor...
    Everything run by electricity will eventually be connected to the Internet. Get ahead of the Internet of Things revolution. In his session at @ThingsExpo, Akvelon expert and IoT industry leader Sergey Grebnov provided an educational dive into the world of managing your home, workplace and all the devices they contain with the power of machine-based AI and intelligent Bot services for a completely streamlined experience.
    SYS-CON Events announced today that Synametrics Technologies will exhibit at SYS-CON's 22nd International Cloud Expo®, which will take place on June 5-7, 2018, at the Javits Center in New York, NY. Synametrics Technologies is a privately held company based in Plainsboro, New Jersey that has been providing solutions for the developer community since 1997. Based on the success of its initial product offerings such as WinSQL, Xeams, SynaMan and Syncrify, Synametrics continues to create and hone inn...