|By Frank Neugebauer||
|March 28, 2003 12:00 AM EST||
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:
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).
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.
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:
Then, you can refer to the attribute set within the <fo:simple-page-master> by using the "xsl:use-attribute-sets" attribute, such as:
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.
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
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.
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).
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.
GENBAND has announced that SageNet is leveraging the Nuvia platform to deliver Unified Communications as a Service (UCaaS) to its large base of retail and enterprise customers. Nuvia’s cloud-based solution provides SageNet’s customers with a full suite of business communications and collaboration tools. Two large national SageNet retail customers have recently signed up to deploy the Nuvia platform and the company will continue to sell the service to new and existing customers. Nuvia’s capabilities include HD voice, video, multimedia messaging, mobility, conferencing, Web collaboration, deskt...
Mar. 29, 2015 01:00 AM EDT Reads: 1,417
The WebRTC Summit 2014 New York, to be held June 9-11, 2015, at the Javits Center in New York, NY, announces that its Call for Papers is open. Topics include all aspects of improving IT delivery by eliminating waste through automated business models leveraging cloud technologies. WebRTC Summit is co-located with 16th International Cloud Expo, @ThingsExpo, Big Data Expo, and DevOps Summit.
Mar. 28, 2015 11:00 PM EDT Reads: 1,499
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
Mar. 28, 2015 08:00 PM EDT Reads: 1,749
SYS-CON Events announced today that Cisco, the worldwide leader in IT that transforms how people connect, communicate and collaborate, has been named “Gold Sponsor” of 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. Cisco makes amazing things happen by connecting the unconnected. Cisco has shaped the future of the Internet by becoming the worldwide leader in transforming how people connect, communicate and collaborate. Cisco and our partners are building the platform for the Internet of Everything by connecting the...
Mar. 28, 2015 07:00 PM EDT Reads: 5,168
Temasys has announced senior management additions to its team. Joining are David Holloway as Vice President of Commercial and Nadine Yap as Vice President of Product. Over the past 12 months Temasys has doubled in size as it adds new customers and expands the development of its Skylink platform. Skylink leads the charge to move WebRTC, traditionally seen as a desktop, browser based technology, to become a ubiquitous web communications technology on web and mobile, as well as Internet of Things compatible devices.
Mar. 28, 2015 06:00 PM EDT Reads: 1,790
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.
Mar. 28, 2015 06:00 PM EDT Reads: 1,433
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...
Mar. 28, 2015 06:00 PM EDT Reads: 1,313
Docker is an excellent platform for organizations interested in running microservices. It offers portability and consistency between development and production environments, quick provisioning times, and a simple way to isolate services. In his session at DevOps Summit at 16th Cloud Expo, Shannon Williams, co-founder of Rancher Labs, will walk through these and other benefits of using Docker to run microservices, and provide an overview of RancherOS, a minimalist distribution of Linux designed expressly to run Docker. He will also discuss Rancher, an orchestration and service discovery platf...
Mar. 28, 2015 04:15 PM EDT Reads: 2,406
SYS-CON Events announced today that Akana, formerly SOA Software, has been named “Bronze Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. Akana’s comprehensive suite of API Management, API Security, Integrated SOA Governance, and Cloud Integration solutions helps businesses accelerate digital transformation by securely extending their reach across multiple channels – mobile, cloud and Internet of Things. Akana enables enterprises to share data as APIs, connect and integrate applications, drive part...
Mar. 28, 2015 04:15 PM EDT Reads: 1,484
SYS-CON Events announced today that Vitria Technology, Inc. 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. Vitria will showcase the company’s new IoT Analytics Platform through live demonstrations at booth #330. Vitria’s IoT Analytics Platform, fully integrated and powered by an operational intelligence engine, enables customers to rapidly build and operationalize advanced analytics to deliver timely business outcomes for use cases across the industrial, enterprise, and consumer segments.
Mar. 28, 2015 03:30 PM EDT Reads: 2,146
SYS-CON Events announced today that Solgenia 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, and the 17th International Cloud Expo®, which will take place on November 3–5, 2015, at the Santa Clara Convention Center in Santa Clara, CA. Solgenia is the global market leader in Cloud Collaboration and Cloud Infrastructure software solutions. Designed to “Bridge the Gap” between Personal and Professional Social, Mobile and Cloud user experiences, our solutions help large and medium-sized organizations dr...
Mar. 28, 2015 03:00 PM EDT Reads: 2,750
SYS-CON Events announced today that Liaison Technologies, a leading provider of data management and integration cloud services and solutions, has been named "Silver Sponsor" of SYS-CON's 16th International Cloud Expo®, which will take place on June 9-11, 2015, at the Javits Center in New York, NY. Liaison Technologies is a recognized market leader in providing cloud-enabled data integration and data management solutions to break down complex information barriers, enabling enterprises to make smarter decisions, faster.
Mar. 28, 2015 03:00 PM EDT Reads: 3,410
Cloud is not a commodity. And no matter what you call it, computing doesn’t come out of the sky. It comes from physical hardware inside brick and mortar facilities connected by hundreds of miles of networking cable. And no two clouds are built the same way. SoftLayer gives you the highest performing cloud infrastructure available. One platform that takes data centers around the world that are full of the widest range of cloud computing options, and then integrates and automates everything. Join SoftLayer on June 9 at 16th Cloud Expo to learn about IBM Cloud's SoftLayer platform, explore se...
Mar. 28, 2015 02:00 PM EDT Reads: 1,599
@ThingsExpo has been named the Top 5 Most Influential M2M Brand by Onalytica in the ‘Machine to Machine: Top 100 Influencers and Brands.' Onalytica analyzed the online debate on M2M by looking at over 85,000 tweets to provide the most influential individuals and brands that drive the discussion. According to Onalytica the "analysis showed a very engaged community with a lot of interactive tweets. The M2M discussion seems to be more fragmented and driven by some of the major brands present in the M2M space. This really allows some room for influential individuals to create more high value inter...
Mar. 28, 2015 12:45 PM EDT Reads: 4,625
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
Mar. 28, 2015 12:00 PM EDT Reads: 1,399
SYS-CON Events announced today the IoT Bootcamp – Jumpstart Your IoT Strategy, being held June 9–10, 2015, in conjunction with 16th Cloud Expo and Internet of @ThingsExpo at the Javits Center in New York City. This is your chance to jumpstart your IoT strategy. Combined with real-world scenarios and use cases, the IoT Bootcamp is not just based on presentations but includes hands-on demos and walkthroughs. We will introduce you to a variety of Do-It-Yourself IoT platforms including Arduino, Raspberry Pi, BeagleBone, Spark and Intel Edison. You will also get an overview of cloud technologies s...
Mar. 28, 2015 11:00 AM EDT Reads: 2,028
SYS-CON Events announced today that SafeLogic has been named “Bag Sponsor” of SYS-CON's 16th International Cloud Expo® New York, which will take place June 9-11, 2015, at the Javits Center in New York City, NY. SafeLogic provides security products for applications in mobile and server/appliance environments. SafeLogic’s flagship product CryptoComply is a FIPS 140-2 validated cryptographic engine designed to secure data on servers, workstations, appliances, mobile devices, and in the Cloud.
Mar. 28, 2015 11:00 AM EDT Reads: 1,372
Containers and microservices have become topics of intense interest throughout the cloud developer and enterprise IT communities. Accordingly, attendees at the upcoming 16th Cloud Expo at the Javits Center in New York June 9-11 will find fresh new content in a new track called PaaS | Containers & Microservices Containers are not being considered for the first time by the cloud community, but a current era of re-consideration has pushed them to the top of the cloud agenda. With the launch of Docker's initial release in March of 2013, interest was revved up several notches. Then late last...
Mar. 28, 2015 09:15 AM EDT Reads: 2,185
SOA Software has changed its name to Akana. With roots in Web Services and SOA Governance, Akana has established itself as a leader in API Management and is expanding into cloud integration as an alternative to the traditional heavyweight enterprise service bus (ESB). The company recently announced that it achieved more than 90% year-over-year growth. As Akana, the company now addresses the evolution and diversification of SOA, unifying security, management, and DevOps across SOA, APIs, microservices, and more.
Mar. 28, 2015 08:30 AM EDT Reads: 2,017
After making a doctor’s appointment via your mobile device, you receive a calendar invite. The day of your appointment, you get a reminder with the doctor’s location and contact information. As you enter the doctor’s exam room, the medical team is equipped with the latest tablet containing your medical history – he or she makes real time updates to your medical file. At the end of your visit, you receive an electronic prescription to your preferred pharmacy and can schedule your next appointment.
Mar. 28, 2015 08:00 AM EDT Reads: 625