XML: The last silver bullet ... It could be just that
- By Jack Vaughan
It is not every day that a writer gets to write about the last silver bullet.
Maybe some would disagree. The software industry takes in and spits out ultimate-savior-technology-to-end-all-technology
silver bullets at a quick rate, and the press writes it all down. So every day
could be silver bullet day. But XML just could be something really different.
This is why....
XML is a marriage that meets the needs of both the democratic Web and the not-so-democratic
software industry. There is no need to ask if these diverse camps can co-exist.
The World Wide Web has already proved that possible. But the folks that brought
you the World Wide Web, inventor Tim Berners-Lee, the W3 Consortium and numerous
others, are a pragmatic lot that are at work on a set of component and semantical
data interchange standards that can be ignored or used. If they are used and
accepted, they may create a design and development environment in which data
and application definitions will be far more flexible than they are today.
It can be hard to get your arms around XML -- the eXtensible Markup Language.
It arises out of SGML and HTML standards efforts, and at first seems to concern
text and document applications. Most products that create XML today come from
the text and document industry.
But coming as it does on the heels of the Web's great success, XML is viewed
by some as having a far broader impact. The way data is handled may be different
if XML catches on. Meta data that describes the data ricocheting around the
development community and the commercial application world today could be the
first areas XML changes. The way applications talk to applications could change.
System management tactics could be affected. In short, XML may have great potential
as smart application server middleware.
In fact, XML is not really a markup language. It might be described as a meta
description of a markup language. You can use it to define your own tags --
something clever developers have wished to do since the beginning of the Web.
HTML's predecessor, SGML, used Document Type Definitions (DTDs) to set the
rules for handling a do-
cument. Later on, Cascading Style Sheets (CSS) applied a somewhat similar principle
to HTML. XML can use DTDs, which may be external or internal. This is a broad-brush
description, but suffice it to say that when properly defined and validated,
XML tags can tell a system something about the data it encounters.
For instance, a schema employed by XML would explain a document's constraints
-- its logical structure. A field such as "last name" [or "dollars"
(or 'pesos')] on an invoice could truly be handled as a last name [or as money]
by other documents that encounter it. The new document would check against a
schema in a repository to find out what the field was meant to represent. But
despite the sense that something useful is near at hand, the usual cautions
New kid on the block
XML really only began in 1996. It is young and immature. And important associated
specifications such as
eXtensible Style Sheets (XSL) and the Resource Description Framework (RDF) Model
are younger still.
The common mantra of XML is that it separates content from presentation. That
is a major difference vs. HTML. You can use XML to direct a markup language
to, in effect, define in-house data handling methods. It allows you to 'normalize'
varied data input sources to allow complex data handling. You can also band
with others to define standards. Or you can use accepted vertical or horizontal
standards that industry groups or vendors manage to agree upon. Acting as a
meta format, and perhaps residing in style sheets sitting in "the great
repository in the sky" (the World Wide Web), XML allows you to change the
definitions of tags as you go forward. Because it is so fluid and decentralized,
it is powerful.
And while flexibility is an XML strength, it can also be a weakness. The idea
that XML is a revolutionary paradigm shift will naturally be challenged. Any
notion that all existing middleware will suddenly give way to XML is silly.
The Object Management Group (OMG), Framingham, Mass., for example, points this
out in a recent white paper on XML. "Every now and then, the computer industry
gets swept up in a wave of enthusiasm for some new silver bullet that's apparently
going to solve everyone's problems overnight," writes the OMG. "[XML]
isn't going to replace solutions like CORBA." The paper outlines XML's
roots in markup languages, and notes that because document content in XML applications
are generally human-readable scripts, XML is likely "a rather inefficient
way of storing information that only ever needs to be machine-readable."
This is a real issue. Truly, it seems early in the game to begin to measure
how good XML performance may be. But the XML effort is, at heart, an attempt
to make the World Wide Web more machine understandable. And the type of stricture
that CORBA-style object programming brings to the table is not widely found
in legacy systems. "Objects are structured. Much of the world isn't. A
lot of what we have to do is apply structure to data that doesn't have it,"
said Dave Robertson, product marketing manager at Redwood Shores, Calif.-based
Constellar Corp., a data hub middleware maker.
Even within the OMG, some use of XML is proposed, at least as a meta data mechanism.
OMG members IBM, Unisys and Oracle are suggesting use of XML
(integrated with another 'ML,' the UML -- the Unified Modeling Language) and
the Meta Object Facility (MOF) as an information interchange model for application
developers. In fact, this use of XML in a meta data format (this particular
proposal is known as XMI), is one of the first big signs of XML's use in application
"There is a broad spectrum of descriptive data that we have to handle,"
said Peter Thomas, product manager for repository technology at Redwood Shores,
Calif.-based Oracle Corp. "XMI is an extensible format, so it can be used
to handle [new] cases. We think it will expand over time." An IBM representative
said XML use means software developers no longer have to resort to proprietary
mechanisms to format the data they are storing in databases or passing between
It is rather forgotten at times that Tim Berners-Lee had a background in object
software technology well before he invented the World Wide Web in 1990. And
his goal, in great part, was to allow information sharing within dispersed teams
of advanced physics researchers and support groups. Much of his work today as
the director of the World Wide Consortium (http://www.w3.org) centers on XML
as a means of extending the exchange of data on the Web.
At the recent Seybold Publishing '99 Conference in Boston, Application Development
Trends asked Berners-Lee what application developers should know about XML.
He responded: "Application developers should be using XML and RDF not just
for Web pages, but also for storing internal files such as configuration files
and, in general, data for exchange."
He continued: "This will allow users to reduce their lock-in to proprietary
formats, and allow them to customize parts of their system while retaining off-the-shelf
products for other parts."
And there is no need to put off some initial work on this effort, maintains
Berners-Lee. "Developers of Web-based applications should be validating
all the HTML they generate against the free test available from W3 (http://validator.w3.org/).
They should also be looking at the upcoming XHTML specification as a transition
from HTML 4.0 to HTML-as XML." In February the Consortium formally released
its RDF specification as a W3C Recommendation.
In the past, complex object models for both development and deployment have
stumbled in finding suitable repository technology. Berners-Lee would be undeterred.
At last year's DCI World e-Business Conference in Boston, he noted: "When
people say we need a repository, we say we have the Web." A repository
should be decentralized, he said. Based simply on his success with the Web,
his statement is hard to counter.
At that same conference, Berners-Lee described XML as "a great pressure-release
valve." This is by way of testament to its ability to support change.
XML's potential has not been lost on industry players -- big or small. Among
the lot of large vendor XML initiatives are two -- from IBM and Microsoft --
that might prove helpful in propelling XML forward.
Microsoft has helped move XML to the forefront via its new browser technology.
Internet Explorer 5.0, released last month, is said to support XML as well as
the XSL that allows developers to apply style sheets to XML data. While it is
now out of beta, browser makers and document builders are still working from
fresh specs, and a shaking out period should still be expected as folks try
to get XML to work consistently. Among early beta users of Microsoft's XML implementation
is Merrill Lynch & Co., which is using XML to improve development time,
usability, data mining and software distribution.
For its part, IBM continues to produce a variety of tools. Editors, transformers,
parsers and Bean makers are just a few of the offerings available as downloadable
technology previews at the IBM alphaWorks Web site (http://www.alphaworks.ibm.com/).
Last month, IBM added Xeena, a syntax-smart Java application for editing valid
XML according to a chosen DTD. XML tools will reportedly become part of future
IBM WebSphere development environments, with application integration as one
of its uses. Last month, IBM announced a deal with The Sabre Group and Noika
to build an interactive service. Sabre is writing a Java application to translate
its travel data into XML so that streams of data can be defined and presented
as individual objects such as airline reservations. (Wireless house Noika will
use IBM software to translate the XML into what is described as a Wireless Markup
Language or WML.)
While support of big players is important, it is a cast of smaller companies
that have set the XML industry in motion. These can be divided, somewhat arbitrarily,
into text-document specialists, data and application development specialists,
and (proving that miscellany still rules) XML- or Web-centric start-ups.
Among text specialists are Arbortext Inc., Interleaf Inc. (which just bought
XML specialty house Texcel Research Inc.), OmniMark Technologies Inc., OpenText
Corp., Softquad Software Inc. and many more.
Among the new breed of companies formed to exploit Web-technology opportunities
that are finding XML a means to that end, place DataChannel Inc., LivePage Corp.,
Perspecta Inc., Sequoia Software Corp., UWI.com, Vignette Corp., WebMethods
Inc. and others.
Among data and application development specialists, Bluestone Software Inc.,
Cloudscape Inc., Inference Corp., Kinetic Technologies Inc., Object Design Inc.,
Poet Software Corp. and others are joining daily. Among this last camp, some
notable XML application development-oriented tools have already been released
this year. In February, Mount Laurel, N.J.-based Bluestone released Bluestone
XML-Server. And in March, Burlington, Mass.-based Object Design announced general
availability of eXcelon, an XML data server.
"eXcelon makes it easier to work with XML," said early eXcelon user
Srini Sankaran, president of Global Automation, a Palo Alto, Calif.-based system
integrator specializing in distributed application integration. "It provides
mapping and some validation. Moreover, it provides scalability."
Is XML revolutionary, we asked. "I don't think it's revolutionary,"
replied Sankaran. "It's really an evolution of SGML for the Web. But its
impact is going to be pretty significant. It's a very natural solution for the
problems of the Web industry."