The State of XML: Why Individuals Matter
This article is adapted from the closing keynote speech I delivered at XML Europe 2001 in Berlin, May 2001. I describe the progress of XML over the last year, emphasizing that in an industry increasingly dominated by large vendors, individual contributors are still key.
XML has a tendency to spark new beginnings. Many existing technologies are being re-engineered to take advantage of XML, gaining interoperability benefits previously too costly to realize; industries are finding that XML vocabularies can form a basis for collaboration and cost-cutting, where such cooperation was previously thought counterproductive. XML's influence is proving disruptive to the technological status quo.
For better or for worse, many parts of today's computing infrastructure are being re-examined in the light of XML. For better, in that the benefit to be gained from interoperability at the syntax level is large. For worse, in that lessons from the past are being overlooked; however, not learning from history is too broad a charge to lay on the shoulders of overzealous XML developers alone.
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Adding XML into your computing environment can be like initiating a chain reaction. Once one component can import, export, or process XML, it becomes obvious that there will be great benefit if the next component does, and the next, and so on. Within organizations and systems, XML is starting to form the basis for a "data bus," where information can flow between applications with less resistance and effort than previously.
To illustrate the diversity of XML's applications, here are just some of the areas XML has moved into recently.
- Distributed computing: SOAP and the XML Protocol work have XML playing an important role as a wire format for intermachine communication, which would have beggared belief a few years ago.
- Configuration: XML is now a popular choice for the humble configuration file, a ready-made, expressive syntax that means developers don't have to worry about creating new syntaxes and parsers for configuration and state files.
- Directory services: The long running DSML effort provides an XML-based version of LDAP, and the recently created UDDI provides a more specific directory service for "web services."
- Storage: WebDAV allows for the storage and management of data in remote filesystems using an XML-based protocol. All major databases now offer some degree of XML storage and searching.
- Page layout: As XSL-FO and SVG near their completion, we now have languages for paginated, precise layout with pointy brackets. It is early days, but XML is making incursions into the world of professional print production.
- HTML: XHTML, particularly XHTML Modularization, is changing the face of web page markup. Merely having well-formed XML in web pages yields many benefits, including easy parsing of pages, and a reliable platform for client-side applications. Interestingly, many of these benefits are being reaped in non-PC-based browsing environments.
- Knowledge management: technologies such as Topic Maps and RDF seek to further construct the "XML data bus" by providing further layers of semantic interoperability. Work is also underway to bring angle brackets to logic and proofs.
Looking at these diverse areas of application, it would seem that little is safe from the attack of the angle brackets -- and this is without looking at the many initiatives in vertical industries to create XML frameworks and vocabularies.
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The progress made by core XML technologies over the last year can be split into three categories: new initiatives, works-in-progress, and completed projects.
New: XML Protocol
The W3C's XML Protocol work is at the center of the most recent "revolutionary" shift in Web computing: web services. Although horribly over-marketed, the central benefit of web services is that they seek to standardize machine-to-machine exchange of XML. In particular, the aim is to make such exchanges easy for application and database developers. The use of XML over HTTP carries with it less overhead and fewer headaches than using the machinery of CORBA or DCOM.
There is a body of opinion that holds that the W3C should have rubber-stamped the SOAP protocol, devised by Microsoft et al., which is already widely deployed and implemented. However, the role played by the XML Protocol Working Group is more crucially a political one, namely, to form industry consensus (i.e. removing the Microsoft stigma), than the strictly technical role of standardization. The unprecedented size of the Working Group -- at my last count it had 84 members, including invited experts -- confirms this suspicion. A lean, mean, spec machine? Doubtful.
New: Semantic Web
For a long time, the Semantic Web has been Tim Berners-Lee's ambition for the future development of the World Wide Web. Enabling the machine-processing of web pages, the aim of the Semantic Web is to make the Web more useful for users. This year, the W3C has officially chartered a Semantic Web Activity.
One of the most immediate tasks of this Activity is fixing the Resource Description Framework (RDF), a core Semantic Web technology which suffers from a poorly written specification, and which has many unresolved issues. An encouraging development is the growing dialogue between the W3C and the developers of Topic Maps applications (who mostly have an SGML/ISO heritage), who are attempting to solve similar problems in semantic representation.
New: Many Verticals
There are now many more applications of XML in specific industry sectors than is possible to keep track of. Not all of these efforts will succeed -- XML is no silver bullet -- but there are beneficial effects of XML's adoption here: hitherto undiscovered possibilities for interoperability with other industries, and cost-savings to be gained from agreement.
As development continues, common chunks of technology across verticals are being factored out, and may soon be available as a platform on which industry-specific applications can be built. Perhaps the most ambitious project to create an underlying platform is ebXML, of which more may be found below.
Getting There: SVG
It has taken its time, but Scalable Vector Graphics in XML is nearly a stable W3C Recommendation. This is exciting news for those to whom high-fidelity graphical representation is important. There are many applications for which the existing range of rendering options is inadequate, e.g. the distribution of engineering drawings.
Another exciting feature of SVG is its small file size compared to bitmap graphics, especially for complex drawings. Combined with its inherent flexibility SVG is a good choice for use on mobile and other compact devices, as well as the desktop browser.
SVG represents the most important step forward in web user interface technology for a long time. The test, as ever, will be in its deployment. There are some excellent implementations of SVG in the field, and it would be great to see SVG make it as a default feature in web browsers.
Getting There: XSL-FO
A styling and pagination language has been in the mind of XML's creators since the beginning. As the work on XSL proceeded, it was decided that the transformation part, XSLT, was immensely useful as a separate technology. While XSLT was being spun off, the formatting objects half of XSL languished a bit. Now formatting objects are reaching maturity too and have the potential to make considerable changes in the way everyday page layout and printing is done.
I was excited to hear of a book written from beginning to end using XML. The author wrote the book's content in XML, then used XSLT to transform to XSL-FO (employing the skills of an external designer to fashion the look of the book in XSL-FO). He then went straight from XSL-FO to PDF, which went to the printer. The XML Europe 2001 conference proceedings were produced in a similar manner. While there is much development to do before XSL-FO can cater to all printing requirements, it's starting to have an impact in low-end applications.
There are other areas of use for XSL-FO. It's been used, for example, to computer-generate printed labels with bar codes. It could also be used within a company in the production of business cards -- most companies still design all their cards by hand, and a change of address could cost a lot of money and time. It's not just in typical document production where XSL-FO could have an impact.
Complete: XML Schema
The completion of the W3C XML Schema Definition Language comes as a relief to many. The most controversial XML technology over the last two years, W3C XML Schema should please most that were involved in the project, but it has never been anything less than a hot potato. At the commencement of the XML Schema work in 1999, everyone was worried that Microsoft would, rather than implementing the nascent spec, continue down its own path with XDR, its proposal for an XML schema language. Happily, Microsoft committed to the W3C route. As XML Schema developed, the focus of the dissent shifted to dissatisfaction with the spec itself: many found the drafts hard to read, others thought XML Schema lacked vital features, others thought that there were too many features.
The political imperative to complete XML Schema proved irresistible, and a (sometimes uneasy) middle ground has been been found. As with XML Protocol, the big story about W3C XML Schema seems more about political consensus than the technical details of the specification itself. Schema provides the hook from XML into databases and programming language data types, which is the missing link for many developers using XML, cutting down the effort required to bind XML into programs as a data transport. Yet at the same time, it carries a worrying risk of increasing XML developers' reliance on external tools in order to abstract away the difficult details of the XML Schema technology. I'll say more about this worry below.
Complete: XML Topic Maps
XML Europe 2001 Conference Report: A Web Less Boring
The completion of the XML Topic Maps specification marks an important step forward for document technologies in XML. It's certainly generated a lot of interest, as well as several new companies. Topic maps technologies are now making their way into mainstream content management solutions. There is a lot yet that the XTM community need to do: education has to be a priority -- many respected XML developers still don't have a clue what a topic map is actually for -- as well as continuing the work on integration with the Web.
The UN/CEFACT and OASIS ebXML project to create an XML framework for global electronic business has now run the course of its chartered eighteen months. During that time it has created a platform on which it is hoped industries can build electronic commerce systems. Given the time constraints, ebXML is by no means finished. It represents a solid start, rather than a conclusion. Work is now continuing in separate working groups chartered by the UN and OASIS.
Providing an alternate approach to the much-hyped web services route, ebXML is tackling a similar problem, but, if you will, from the other end. It is hoped that the overarching framework from ebXML and the low-level web services technology will meet to complement each other. Much implementation experience is required, and during that process the more ambitious (or even unrealistic) aims will be tempered.
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