The XSL-FO 1.0 Recommendation is now more than a year old, and it's exciting to see a number of commercial implementations and open-source or free projects available for the Extensible Stylesheet Language Formatting Objects. One such implementation is at Crane Softwrights Ltd., where XSL-FO is used extensively on a daily basis for quality print-oriented results.

Formatting objects express the semantics of paginated formatting intent. To get professional-quality print results from XML, you transform XML instances into instances of the XML vocabulary that has been associated with the formatting semantics. Much as you'd transform your XML instances into instances of HTML for display in Web browsers, XSL-FO formatting engines interpret your intent expressed in instances of the XSL-FO XML vocabulary to produce a paginated result.

Pagination differs from the infinite-length, variable-width browser screens we've become so very used to working with. But for many developers, paginated, page-based, fixed-size-folio printable results have been left by the wayside while they focus on the HTML displays they're comfortable with. This, unfortunately, leaves a whole constituency of potential users of Web services and XML-encoded information disenfranchised. Think of those nondevelopers you know who still rely on the printed form, perhaps printing out every e-mail message or every Web screen so they can better comprehend what they're reading - they're hindered not by the content, but by the medium.

Consider also how simple requests can often result in copious amounts of information, or how many volumes of information you may have that you need to disseminate. How many people are truly satisfied with their information experience when dealing with a printed Web screen? How can you expect to properly navigate such a volume of data and ensure your users have the easiest access to the amount they have to deal with?

The semantics of pagination improve the printed result over the dynamic browser screen print function because of the nature of how the reader consumes information in these two very different environments. Navigation in the browser experience is automated; the reader of a Web screen need not know where hyperlinks to information are to be able to successfully change focus to a new location within the information set, because the browser is responsible for traversing the link. Navigation in the printed form is the responsibility of the human reading the pages. This burdens the publisher with providing navigational hints to the reader to make the reading experience easy and obstacle free. Common navigation tools used for the printed form include headers, footers, page numbers, and page-number citations. Judicious design and use of these tools by the publisher will make the message more easily accessible to the human audience.

The partner to XSL-FO is the Extensible Stylesheet Language Transformations (XSLT) Recommendation, though these two standards are surely not wedded together. Although the predominant use of XSL-FO will result from the transformation of XML information using XSLT, XSL-FO engines will work on any XML instance of the pagination vocabulary regardless of how it is generated. You can regard XSL-FO as a layout language of the printed form regardless of the programming language, database extraction, or document editing tool used. Indeed, the free AbiWord word processor has already implemented a "Save As XSL-FO" function. There is also a free resource on Crane's Web site for the dumping and display of Unicode characters and their hexadecimal code points using a Python program to directly generate an instance of XSL-FO XML for rendering by an XSL-FO engine, without any use of XSLT.

XSL-FO in the Real World
In addition to helping to serve the wonderful world of Web services to a whole new audience, XSL-FO opens doors for both the traditional publishing experience and new publishing paradigms.

Crane Softwrights Ltd. authors and publishes training material for XML technologies. Our two flagship products are "Practical Transformation Using XSLT and XPath" and "Practical Formatting Using XSL-FO." The first editions of these electronic publications predate all of the paper publications in each of these two subjects.

In our view of this new publishing paradigm, XML technologies play a critical role in making publishing efforts successful. XSLT is used to leverage a single-authored set of content into instructor-led training material for us and for our licensees around the world (creating both HTML projection slides and paper handouts), and for commercial book publishing in both electronic and paper forms. XSL-FO and XSLT are used at Crane to produce 11 electronic renditions of each book: five in a U.S. letter paper size PDF, five in an international A4 paper size PDF, and one in a hyperlinked, monospaced accessible presentation suitable for unsighted customers using on-screen text readers. Two full-size renditions of the PDF files are also richly hyperlinked, allowing successful navigation in paper form and electronically in a PDF viewer.

In this publishing scenario, the negligible cost of publishing new editions for existing customers allows customers to enjoy perpetual no-charge updates for future editions of the titles that they purchase. Free previews are downloadable from Crane's Web site and licenses are sold to individuals; a single geographic site license and a worldwide license for staff members of a company are available.

This leverage extends to the traditional publishing experience. Prentice Hall has purchased the print rights to each book Crane sells electronically, producing the paper-based renditions as Definitive XSLT and XPath and Definitive XSL-FO. The XML content is delivered directly from Crane to editor Dmitry Kirsanov, who polishes up the English to Prentice Hall standards, produces a print image using his own XSL-FO stylesheets, and delivers to Prentice Hall the fully composed PDF file ready for reproduction. We believe Definitive XSLT and XPath is the very first paper-based commercial trade book publication produced with XSL-FO.

The leverage promised by XML is realized after the first book is done and the second and subsequent books are produced. As we create new training materials, we reuse the XSLT and XSL-FO stylesheets and production environment for all of the target uses for training. We then publish the materials commercially from our Web site. If the topic is of interest in the print world, the Prentice Hall-styled stylesheets are ready for use for the document model created for our title.

XSL-FO and Our Choices
XSL-FO gives us the power to give our users information in an alternative presentation than we've used in the past with Web browsers. This increases the consumption of large amounts of information by providing well-known navigation tools consistent with other sources of information our users take advantage of.

The traditional promise of XML publishing, one source with many target formats and audiences, can be realized in the printed medium with XSL-FO, producing professional results. Consider how you can integrate traditional publishing responsibilities (user manuals, reports, etc.) with your powerful new XML information systems to produce a self-consistent multimedia collection of integrated information assets.

The new promise of Web services can reach a new audience or give an existing audience a choice in how to accept large amounts of information, giving users a better information experience and more value. Consider how you can integrate on-the-fly PDF generation as part of your service offering.

We developers may have been reluctant to address the print medium in favor of dynamic displays and may have been postponing addressing our traditional publishing requirements while we have been exploring the power XML gives us in marshaling our information. Now that printable results can be easily produced using XSL-FO, we should be considering the role that automated pagination can play in rounding out our offerings with quality print products while further leveraging our investment in markup.

Resources

Dmitry Kirsanov: www.kirsanov.com

Published Jan. 3, 2003— Reads 6,767
Copyright © 2003 SYS-CON Media, Inc. — All Rights Reserved.
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About G. Ken Holman
G. Ken Holman is the chief technology officer of Crane Softwrights Ltd., current Canadian chair of the ISO subcommittee responsible for the SGML family of standards, an invited expert to the W3C, and member of the W3C Working Group that developed XML from SGML. Ken is the author of electronically published and print-published books on XML-related technologies, and a frequent conference speaker.