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<td bgcolor="#cc0000" valign="bottom" width="361" height="35">来自: www.nature.com</td>
<td align="right" valign="bottom" bgcolor="#CC0000" height="35" width="323"><font face="times, times new roman, serif" size="3" color="#FFFFFF">1 October 1998</font></td>
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<!-- BODY TEXT STARTS HERE --> <font face="times, times new roman, serif" size="5"><b>The
XML Revolution</b></font>
<p> <font face="helvetica, arial, sans serif" size="3"> <a href="#Dan">DAN
CONNOLLY</a></font>
<p>
<font face="times, times new roman, serif" size="3"> If you have ever peeked
with the 'view source' option on your Web browser, then you're familiar
with Hypertext Markup Language (HTML).
<p> HTML was an overwhelming success because it fulfilled a dream that word
processors, despite their myriad features, do not<a href="#1"><sup>1</sup></a>.
So,
<blockquote> "pick up your pen, mouse or favorite pointing device and press
it on a reference in this document -- perhaps to the author's name, or
organization, or some related work. Suppose you are directly presented
with the background material -- other papers, the author's coordinates,
the organization's address and its entire telephone directory. Suppose
each of these documents has the same property of being linked to other
original documents all over the world. You would have at your fingertips
all you need to know about electronic publishing, high-energy physics
or for that matter Asian culture. If you are reading this article on paper,
you can only dream, but read on." </blockquote>
<p> Now that dream is a reality, and human communication is vastly augmented
by the Web: that is, as long as the communication consists of a title,
headings, paragraphs, lists, tables and forms.
<p> What about all the other communications idioms and document types that
we routinely use to get our work, business, and play done?
<ul>
<li> Restaurant menus
<li> Theatre programmes
<li> Meeting minutes, with agenda items and actions
<li> Cheques, invoices and purchase orders
<li> Calendars and project schedules
</ul>
<p> Extensible Markup Lanuage (XML) is the evolutionary successor to HTML,
in that "less is more". If you're thinking that XML is all the stuff from
HTML plus a few more things, think again. It's the same pointy-brackets,
tags, and attributes; but when it comes to tag names, the slate is wiped
clean. XML is like HTML with the training wheels off.
<p> Of course, you can imitate menus, programs and schedules with HTML,
or you can put pictures or facsimiles of their traditional printed form
on the Web. That's great because it allows you to share them with people
all over the planet instantly. But it doesn't invite the computer to help
you manage them.
<p> The bane of my existence is doing things that I know the computer could
do for me.
<p> If the Web page with your personal calendar says you'll be in New York
next Thursday, and the page with your workgroup calendar says you'll be
in London all week, shouldn't the computer be able to warn you about the
conflict? And shouldn't it go ahead and ask you if it's OK to cancel your
flight to London and purchase this other ticket to New York?
<p> As a medium for human communication, the Web has reached critical mass
(I won't go so far as to say it's mature--there's plenty of work still
to be done) but as a mechanism to exploit the power of computing in our
every-day life, the Web is in its infancy. The Web now allows us to communicate
our problems to one another faster than ever before, but does it really
help us solve them?
<p> XML is so simple that it just might work: it might revolutionize the
ability of people to conduct commerce, express themselves, and generally
get work done with computers and networks.
<p> Website designers are doing some amazing things, but they often reinvent
the wheel for any number of reasons. Order-processing systems make a good
example: some web design shop, say <tt>mall.com</tt>, built one shopping-cart
system, but <tt>mousetraps.com</tt> can't use it, because
<ul>
<li> their infrastructure is Windows NT, and the <tt>mall.com</tt> system
is based on Unix, or
<li> Perl vs Java, or perhaps
<li> the <tt>mousetraps.com</tt> folks were just too busy to discover
that <tt>mall.com</tt> had solved the problem, or
<li> the <tt>mall.com</tt> system is aimed at a million transactions per
day and requires thousands of dollars worth of hardware and software,
while the <tt>mousetraps.com</tt> folks only expect a few orders a week
and can only afford a few hundred dollars, or
<li> <tt>mall.com</tt> doesn't care to share its technology with the community
either because
<ul>
<li> they don't want to lose a competitive advantage or
<li> because they don't want to take on a support burden.
</ul>
</ul>
<p> For all these reasons, it takes longer to develop effective websites
than it should, and the community is looking for opportunities to share
technologies and resources.
<p> At the lowest level, organizations like the World Wide Web Consortium
(<a href="../../../www.w3.org/index.htm" tppabs="http://www.w3.org/">W3C</a>), The Internet Engineering Task
Force (<a href="../../../www.ietf.org/index.htm" tppabs="http://www.ietf.org/">IETF</a>) and The Object Management
Group (<a href="../../../www.omg.org/index.htm" tppabs="http://www.omg.org/">OMG</a>) are engaged in updating
the transport infrastructure, <a href="../../../www3.org/Protocols/index.htm" tppabs="http://www3.org/Protocols/">HTTP</a>.
The aims are first to address some of the design shortcomings that 5 years
of experience has exposed, and second to integrate better with modern
software development. At the next level, the software development community
is pushing the Web down into the infrastructure of operating systems and
languages like Perl, Java, and Microsoft Windows. The goal of all this
low-level stuff is that it "just works," like a lightswitch or a telephone.
<p> But there's a twist: along with shipping your pages around, the computing
infrastructure should take every opportunity to read, understand, and
act on them. There's no reason to live with the status quo<a href="#2"><sup>2</sup></a>:
<blockquote> "Hospitals have begun to offer the [home health care] agencies
a solution that goes something like this:
<ol>
<li> Log into the hospital's Web site.
<li> Become an authorized user.
<li> Access the patient's medical records using a Web browser.
<li> Print out the records from the browser.
<li> Manually key in the data from the printouts.
</ol>
<p> The knowledgeable reader may smile at this "solution," but in fact
this is not a joke; this is an actual proposal from a large American
hospital known for its early adoption of advanced medical information
systems."
</blockquote>
<p> <em>Manually key in the data</em>? Can't the two systems be made to
talk to each other? Never mind the multibillion-dollar medical industry;
how often do you get a computer-generated bill, invoice, or airline ticket,
and then manually key the information into your computer to manage your
schedule or finances? Is this the best we can do? Not if the XML revolution
succeeds.
<p> Today, several major Web search services build big indexes. These are
incredibly useful, but they're also limited: they don't know the difference
between a book <em>by</em> Ben Franklin and a book <em>about</em> Ben
Franklin, let alone the difference between an African beetle and a Volkswagen
Beetle.
<p> The search services <em>do</em> know which part of your page is the
title, because the <tt><title> </tt>tag in the HTML markup tells
them. Why not just add <tt><by></tt> and <tt><about></tt>
and <tt><genus></tt> and such tags to HTML? Because
<ul>
<li> technically, it would produce a mess: HTML is hard enough to process
now, and if we make it harder, we reduce the chance that new tools will
come along and make the Web smarter.
<li> socially, it wouldn't work: the HTML specification is maintained
by a small group of experts who are trusted to Do The Right Thing on
behalf of the community; that small group doesn't have expertise in
all subjects that may be covered by Web pages, and if we added that
expertise to the group, it would be too large to function. It is much
better to give everyone a tool that they can easily adapt for their
own particular needs.
</ul>
<p> HTML was a critical first step, but it is, by design, a one-size-fits-all
solution; it works well when applied to its original domain of simple
structured documents with links, but doesn't work so well in all the other
domains where people want the Web to apply.
<p> XML, like the Internet and the Web, is designed to facilitate a marketplace
of competing companies, innovative individuals, and organizations of all
sizes in between. <a href="../../../www.w3.org/index.htm" tppabs="http://www.w3.org/">W3C</a> is a consortium
of 270+ member organizations committed to the growth of this marketplace,
ensuring interoperability and smooth evolution.
<p> This decentralized marketplace is already at work: to automate the exchange
of bills, statements, and payments, the banking and software heavyweights
are working on Open Financial Exchange (<a href="../../../www.oasis-open.org/cover/gen-apps.html#ofe#xml-ofe" tppabs="http://www.oasis-open.org/cover/gen-apps.html#ofe#xml-ofe">OFX</a>);
meanwhile, to automate exchange of information about chemicals, their
properties, uses and suppliers, one researcher in Nottingham, Peter Murray-Rust,
rolled up his sleeves, and Chemical Markup Language (<a href="../../../www.oasis-open.org/cover/gen-apps.html#cml" tppabs="http://www.oasis-open.org/cover/gen-apps.html#cml">CML</a>)
was born.
<p> XML is intended to span this wide spectrum of application, and it has
become a strategic technology in W3C, where members are sharing resources
to compliment HTML with XML-based technologies:
<ul>
<li> <a href=" ../../../www.w3.org/Math/index.htm" tppabs="http://www.w3.org/Math/">MathML</a>, for describing mathematics
as a basis for machine-to-machine communication.
<li> <a href=" ../../../www.w3.org/AudioVideo/index.htm#SMIL" tppabs="http://www.w3.org/AudioVideo/#SMIL">SMIL</a>, for expressing
media synchronization
<li> <a href=" ../../../www.w3.org/RDF/index.htm" tppabs="http://www.w3.org/RDF/">RDF</a>, for resource description,
such as library-style cataloging
<li> <a href=" ../../../www.w3.org/P3P/index.htm" tppabs="http://www.w3.org/P3P/">P3P</a>, to use XML and RDF so
users can be informed, in control, and make decisions based on their
individual privacy preferences.
</ul>
<p> XML by itself is just a simple text format; but together with all the
ways it's being used to share structured information, it's a revolution
that promises to make the Web a whole lot smarter.
<p>
<hr width="50%" size="2">
<p> <b>References</b> <a name="1">1. </a>Berners-Lee, T., <i>et al</i>.
<a href="../../../www.w3.org/History/1992/ENRAP/Article_9202.ps" tppabs="http://www.w3.org/History/1992/ENRAP/Article_9202.ps">World-Wide
Web: The Information Universe</a> in <i>Electronic Networking: Research,
Applications and Policy</i> <b>1</b> 2 (Meckler, Westport CT, USA, 1992)
<p> <a name="2">2.</a> Bosak, J. <a href="../../../sunsite.unc.edu/pub/sun-info/standards/xml/why/xmlapps.htm" tppabs="http://sunsite.unc.edu/pub/sun-info/standards/xml/why/xmlapps.htm">XML,
Java, and the future of the Web.</a> <i>Sun Microsystems</i> (c. 1 Oct
98) http://sunsite.unc.edu/pub/sun-info/standards/xml/why/xmlapps.htm
(1997).
<p>
<p> <em><a name="Dan"></a>Dan Connolly is the leader of the <a href="../../../www.w3.org/Architecture" tppabs="http://www.w3.org/Architecture">W3C
Architecture Domain</a>. He collaborated with Jon Bosak to form the W3C
<a href="../../../www.w3.org/XML/index.htm" tppabs="http://www.w3.org/XML/">XML</a> Working Group and produce the
W3C XML 1.0 Recommendation. <!-- BODY TEXT ENDS HERE --> </em>
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<font face="geneva, arial, sans serif" size="2">Nature © Macmillan
Publishers Ltd 1998 Registered No. 785998 England.</font></td>
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<p>返回: <a href="philosophy.htm" tppabs="http://www.xml.org.cn:8188/resource/article/philosophy.htm">XML的哲学思考</a> 编者: 朱麟 <br>
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