When I first started writing about XML (Extensible Markup Language) four years ago, there really wasn't much to it. XML's simplicity was both a deliberate choice and a very good thing. A small community of highly opinionated people were available to help out with all kinds of questions, and it actually seemed plausible to attempt to explain XML and its potential in a reasonably short book. Today, nearly three years after XML 1.0 became a W3C (World Wide Web Consortium) recommendation, XML 1.0 has grown to the point where trying to describe the XML family of specifications is nearly impossible.
XML's buzzword status contributed to a fantastic growth of supporting standards, but that growth is now threatening the ease with which people approach XML. Newcomers wandering into XML find themselves confronted with namespaces, schemas, transformations, and a variety of APIs, plus new features like XML Base and XML Inclusions. By a quick count of the W3C's Technical Reports page, limited to active working drafts and various stages of recommendations, there are approximately 15 core XML specifications, 14 specs on processing XML, 20 specs on styling XML, 14 specs related to XHTML, 21 specs about applications of XML, two specs about RDF metadata, and three specs on XML linking technologies.
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Complicating matters further, the offerings from the W3C are no longer the only game in town. Developers interested in working with schemas can choose from XML 1.0 DTDs (Document Type Definitions), the W3C's XML Schema Description Language (Primer, Structures, Datatypes), Microsoft's XML Data-Reduced, and SOX, RELAX, Schematron, and now TREX, among others.
For metadata, the W3C's own Resource Description Framework (RDF) and XML Linking (XLink) have some areas in common, while Topic Maps, a third contender, offers yet another means of describing and connecting information. The three specfications address different needs, but have significant overlap.
In styling, the W3C offers two different approaches, Cascading Style Sheets (CSS) and Extensible Stylesheet Language (XSL). Amidst this plenty, a number of developer groups, notably the SML-Dev mailing list, have worked on simplifying XML, but even these projects add to the overall number of specifications.
Industry-specific vocabularies and protocols built on XML add even more to the mix, as does the work of consortiums like OASIS. While the XML community has developed resources for finding resources--like Robin Cover's XML Cover Pages, an extensive bibliography, XML.com's Resource Guide, and news sites like xmlhack.com, not to mention BizTalk.org and XML.org--figuring out where to get started can be very difficult. While standardized vocabularies and structures are available for some areas, they don't answer every need.
So what is O'Reilly doing to make sense of the XML space? We're forging ahead in three areas: online, conferences, and books.
XML in a Nutshell, a comprehensive, easy-to-access desktop reference to the fundamental rules that all XML documents and authors must adhere to.
Learning XML explains XML and its capabilities succinctly, with references to real-life projects and other cogent examples.
XML Pocket Reference, 2nd Edition, is both a handy introduction to XML terminology and syntax, and a quick reference to XML instructions, attributes, entities, and datatypes.
We've also published the first of many books that cast a wider net and bring specific technologies into sharp focus for XML developers. Titles available are:
Java and XML shows how to put the two together, building real-world applications in which both the code and the data are truly portable.
Building Oracle XML Applications gives Java and PL/SQL developers a rich and detailed look at the many tools Oracle provides to support XML development.
DocBook: The Definitive Guide contains an introduction to SGML, XML, and the DocBook DTD, plus the complete reference information for DocBook.
Several of our XML books are also available on Safari: O'Reilly Books Online, our subscription-based online book service. Safari is updated with new books weekly, so check back often if you're not already subscribed.
Simon St.Laurent is an associate editor with O'Reilly & Associates. Simon's books include XML: A Primer, Second Edition (IDG Books), XML Elements of Style (Osborne), and Building XML Applications (Osborne). He is a contributing editor to xmlhack.com and an occasional contributor to XML.com.
Copyright © 2007 O'Reilly Media, Inc.