We commemorate the progress of "markup" in modern times on two special days: October 15, 1986 marked the official publication of ISO 8879: Standard Generalized Markup Language, while February 10, 1998 saw the official publication of SGML's (hitherto) most successful profile, the W3C Recommendation Extensible Markup Language (XML) 1.0. Originally conceived as means of allowing "generic SGML to be served, received, and processed on the Web in the way that is now possible with HTML," XML has expanded far beyond the boundaries of its original intent, coming to serve many purposes other than structured data interchange.

Dave Hollander and C. M. Sperberg-McQueen, participants in the W3C XML Working Group which produced the first W3C XML Recommendation, have written an essay "Happy Birthday, XML!" which reflects upon the progress of the Extensible Markup Language . They conclude with a question that now occupies the mind of many: "So, now that XML is five, where do we go from here?"

Jon Bosak (frequently referred to as "The Father of XML") has also composed personal reflections appropriate to Happy birthday, XML! He notes that "The five years since XML was released have seen XML become the lingua franca of the Web, but this universal embrace has not always been accompanied by a clear understanding of what XML can and cannot do..." See the full context for these comments on the limited potential of XML to magically (of itself) solve modern problems of data interoperability.

Representing a later generation of XML expert developers -- including watchdogs, revisionists, late-night hackers -- Edd Dumbill of XML.com has written a birthday commentary on the XML specification which has exceeded all initial expectations. In "XML at Five", Edd provides entertaining, illuminating, and thought-provoking comments from "some XML old-hands and friends of XML.com" based upon experience with XML over the last five years. "During those five years, XML.com has followed the XML world tirelessly, publishing nearly a thousand articles and becoming a forum for the heart of the XML community itself."

Goals of XML

[Excerpts from Sperberg-McQueen and Hollander]

Just as interchangeable parts drove the Industrial Age, reusable information powers the Information Age. Our shared experience with SGML had taught us that information becomes more valuable when it can be shared and reused. And the Web would let us share information with wider audiences than we ever imagined. We knew that SGML was the best approach for reusing the kinds of information we worked with, but we needed to make SGML easier to learn, understand, and implement, while retaining its core values; in short, SGML fit for the Web.

The core value of SGML that we wanted to build into XML is that of descriptive markup. Markup is information inserted into a document that computers use; in the case of SGML, markup takes the form of tags inserted into documents to mark their structure. Descriptive markup uses markup to label the structure and other properties of information in a way that is independent of both the system it's created on and of the processing to be performed on it.

We did not want XML to be a fixed set of tags: we wanted XML, like SGML, to be a meta-language. Meta-languages are languages used to create vocabularies and that that are relevant to their information. User defined, processing-independent markup is easier to reuse and can be processed in new and often unexpected ways.

Like SGML, XML was intended to help information owners escape being locked in to a particular vendor .Descriptive markup also makes information independent of any particular piece of software. System-dependent and proprietary formats hinder the reuse of information and make the data owner dependent on the vendors whose software can create and manipulate those formats.

By making SGML fit for the Web, it would be easy and reliable for computers (and humans) to use descriptive, structural markup in their documents. By tagging data descriptively, the information owner can make documents into semantically rich data and avoid the kind of presentation-oriented markup used just because it looks right, markup we called 'crufty tag salad'.

XML Pioneers and Followers

XML took its impetus (and syntax, for better or worse) from SGML. From among a host of meta-markup system designers and visionaries having influence in both initiatives, Charles F. Goldfarb and Yuri Rubinsky represent icons of pathfinding. In the early days -- before markup became prostituted by marketing (DTDs apparently written as marketing collateral) and hawked by charlatans (soothsayers masquerading as analysts) -- it was difficult to find business executives willing to listen to the "descriptive markup" story. XML has made all the difference: in recent times, as noted by Tim Bray (co-editor of XML 1.0, aka "godfather of XML"), XML is more conspicuous by its absence than by its presence.

The First XML Cup Award was given to James Clark, who continues to provide the markup community with technical leadership and tools. The Second XML Cup Award was presented to Jon Bosak and Tim Bray; both were co-editors of the XML 1.0 Recommendation and continue to exert an influential role in the adoption and refinement of XML languages (Jon Bosak: Universal Business Language; Tim Bray: W3C Technical Architecture Group - TAG).

Michael Sperberg-McQueen, co-editor of the XML 1.0 Recommendation and of the TEI Guidelines, provides leadership through his role as Domain Leader for the W3C's Architecture Domain, which subsumes the W3C XML Activity. The third co-editor of the XML 1.0 Recommendation, Microsoft's Jean Paoli, continues to lead design initiatives for the incorporation of XML technologies into office applications.

Of course, XML was not designed by just three editors, nor even by a group of twelve, nor by eighteen -- as listed for the W3C XML Working Group (WG). The XML-SIG numbered some fifty-eight (58) members in the list of August 28, 1996, and then 137 in Jon Bosak's roster of July 2, 1997. XML was "designed" by a community, and its five-year progress has been influenced by the dedication and cooperation of hundreds.

Today, the Worldwide Web Consortium (W3C) is XML's official custodian. Led by Tim Berners-Lee and host of experts, W3C continues to be the principal official locus of XML engineering for core XML-related specifications. Unofficially, a group of XML Deviants tries to keep the W3C attentive to concerns of developers and small companies; their writings are summarized in XML.com's "XML Deviant" column" and in postings to the XML-DEV mailing list, archived at OASIS.

The result: XML applications abound, numbering in the thousands; specifications using XML for interchange and structural representation continue to be produced within all standards frameworks, including IETF, ISO, OASIS, UN/CEFACT, and W3C. One of the many ironies: the simplicity and accessibility of XML as a notation (despite the perspective that XML is not a good data modeling formalism) has arguably increased the number of formal specifications designed to support interoperable computing solutions.

Commentary

Everyone has a personal opinion about the quintessence of XML as a meta-markup language. Some of us have a different guess each day. Today's guess: "XML means being explicit about your (descriptive, prescriptive) intent and in your assertions. Being explicit rather than implicit is essential for machines, and greatly enhances the quality of human communication as well."

Markup design became conscious and formal in the 1960s (arguably in the 1950s), but that's just a modern analytical perspective. A form of markup (exploiting end-tag omission, XML-reduced) was used in the writing systems of Sumerian and Akkadian, second millennium BCE. More than 4000 years ago, before machines did the computing.