ONCE, Web search engines were a wonder. Just by entering a keyword you could
sift through millions of pages in seconds to hunt down the information you
needed. Nowadays, it鈥檚 a wonder anyone bothers. The Internet has grown so vast
and varied that it鈥檚 not unusual for a search to throw up 10 000 hits. You
almost need another search engine to discover anything useful.
Worse still, even though thousands of pages contain your keyword, the chances
are that many do not use the word in the sense you want. Search for 鈥済ates鈥�, and
you鈥檒l receive links to pages about the tiny silicon gates on transistors, the
five-barred variety found on farms and, of course, Bill Gates. The fact is that
the Web is pretty stupid when it comes to 鈥渦nderstanding鈥� the information it
conveys.
The problem lies with the language that weaves the Web, HyperText Markup
Language (HTML). It began life at CERN, the European laboratory for particle
physics, where Tim Berners-Lee wanted an easy way for his colleagues to post
their papers online. The simplicity of his solution unexpectedly triggered the
revolution that has made the Net so popular today. Yet, at the same time,
growing competition between software companies to make the Net ever more
seductive and powerful has pushed HTML far beyond what it was designed to cope
with.
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Today, however, a second revolution is under way鈥攐nly this time it鈥檚
being planned. A new Net language, called the Extensible Markup Language (XML),
promises to make the Web smarter by including machine-readable information about
the structure and content of Web pages. Search engines, then, will be able to
home in on just one meaning of a word.
But that鈥檚 not all. XML opens the door to new languages that will allow
musical notation and mathematical and chemical symbols to be sent across the Web
as easily as text. Documents written in these languages will be interactive in
ways we can only dream about today. Readers will be able to treat the
information in these documents just like raw data鈥攁nalysing or
manipulating it any way they see fit.
Wildest dreams
XML should be good for industry too. As the Web grows smarter, that
Cinderella of electronic communications, e-commerce, will finally get to the
ball. 鈥淭here are loads of start-up companies with pockets bulging with venture
capital hoping to make this work,鈥� says Tim Bray, a founder of the XML working
group at the World Wide Web Consortium, the nearest thing the Web has to a
controlling body.
The consortium published XML 1.0 last December (http://www.w3c.org/XML/).
Since then, software companies around the world have raced to apply it in
almost every area of computing. 鈥淣one of us could have predicted the events of
the past few months in our wildest dreams,鈥� says Bray. Amid all this turmoil,
the general shape of the XML Web is slowly starting to emerge.
The language that has brought the Web this far, HTML, is a 鈥渕arkup鈥� language,
consisting of text interspersed with tags, normally in pairs and contained
within angled brackets. These tags mark out the underlying structure of the
document. So, for example, a Web browser will interpret whatever is between the
and
tags as a major heading, and will usually display it in large,
bold type.
Berners-Lee kept the tags basic and their number low. As a result, HTML
conveys only a tiny amount of information about documents it marks. This is not
the case with XML, which is a 鈥渕etalanguage鈥�: it provides a set of rules for
constructing other markup languages. As such, it lets people make up their own
tags (hence the 鈥渆xtensible鈥� in the title), and so can provide much richer
information about the data held in documents.
Smart search
This 鈥渕etadata鈥濃�攄ata about data鈥攎ight include information about
the subject matter of Web pages. With XML, attaching metadata to a document is
easy, at least in theory. Back with our 鈥済ates鈥� query, the range of subject
matter would include electronics, farming and billionaires. The appropriate
choice could be placed between a new pair of tags,
example, which would allow a search engine to 鈥渦nderstand鈥� it鈥攁t least to
the extent of knowing which kind of gates it is dealing with. So when you
searched, hits would be presented grouped by subject rather than a random
mix.
But this begs two big questions. What will all the extra tags on an XML page
look like when viewed through a Web browser which can cope only with
presentational tags such as title and heading? And if everyone is making up
their own tags, how will search engines know what they refer to? The answers to
these questions highlight fundamental differences between HTML and XML.
It is a basic rule of XML that content and presentation are separate. So XML
tags contain no hint about how they should be displayed. This means that in
future, before you can read an XML page it will have to pass through a program
that will format it for you. These programs generally use 鈥渟tylesheets鈥�. And one
candidates for creating stylesheets uses an XML language called eXtensible Style
Language (http://www.w3c.org/Style/XSL/).
Stylesheets are equivalent to the templates already used in wordprocessors to
give documents the same look, says P. G. Bartlett, vice-president of marketing
at the Michigan-based software company ArborText, which has done much of the
work defining XSL. These stylesheets consist of formatting rules for how
particular XML tags, such as
page. One obvious approach would be to use a stylesheet to convert XML tags into
HTML tags, so that a document could be viewed with a Web browser.
But XSL promises much more. 鈥淒ifferent stylesheets can be applied to the same
data,鈥� says Bartlett. Parts of a document, separated by different tags, could be
hidden or displayed by different stylesheets. A page could contain three
versions of the same product information, for example: one for a company鈥檚
managers, another for its engineers and the third for its customers. Each
version would be revealed by a different stylesheet, says Bartlett.
While XML and XSL revolutionise the way the Web deals with the content and
look of information, another XML application, called XLink, offers an
invigorating update to that other key feature of the Web鈥攈yperlinks (
http://www.w3c.org/TR/1998/WD-xlink-19980303). XLink will introduce a
number of novelties, says Eve Maler of ArborText, co-editor of XLink. 鈥淵ou could
target a particular chunk of content such as a section, rather than pointing to
a whole 诲辞肠耻尘别苍迟.鈥� This is possible because XLink allows extra information to be
added to Web addresses. You could create a hyper-link, for example, that
would take you to the third speech of the second scene of the second act of a
play (see Diagram on page 36).
You can also make your links 鈥渂ehave鈥� in strange ways on screen, says Maler.
Say you鈥檙e reading a guide to hotels and the hyperlinks come in two
varieties鈥攃ontact details for the hotels and maps showing their locations.
Place the cursor over the hotel name and a line of XLink code will turn it red
if it takes you to a map and green for the contact details. And all before you
click the mouse. Better still, XLink could give you a pulldown menu of the
options.
For all this array of possibilities, our second big question remains: if
Website designers can invent XML tags, how will search engines know what they
all 鈥渕ean鈥�? Fortunately, XML comes complete with its own solution to this
problem, called the Resource Description Framework
(http://www.w3.org/RDF/Overview.html).
RDF allows information about a Web page to be stored as if in a structured
database. Using an XML tag such as
metadata, says Bray. Our gates example might include things such as farming,
agriculture, fencing, wood, and so on. While a human can understand this kind of
list, a machine cannot. By contrast, RDF could be employed to divide up metadata
into fields such as 鈥渕ain subject鈥� and 鈥渟econdary subject鈥濃�攁nd you could
use the secondary subject tag more than once. Other tags might include 鈥渄ocument
author鈥� and 鈥渄ate of creation鈥�. This allows search engines to get smarter in
future. Asked to find all documents written by Joe Bloggs about bananas before
December 1997, a smart search engine would check the author and subject and then
ask if the date is less than or equal to 30/11/97.
RDF itself does not specify names for the fields鈥攊t merely sets out the
syntax for how different fields relate to Web pages and to one another. It is up
to different groups of users to name the fields and decide which collections of
fields鈥攐r schemata鈥攁re best for them. 鈥淪ome communities will define
`official鈥� schemata,鈥� says Ora Lassila of the Nokia Research Center in Boston
and co-editor of the RDF standard. 鈥淔or example, the library community is
working on its Dublin Core schema.鈥� The Dublin Core schema consists of 15 fields
that give all the basic information about electronic documents. They include
title, subject, creator, publisher and date of creation.
鈥淭he problem with official schemata,鈥� says Lassila, 鈥渋s that it takes a long
time to get enough representatives from any community to agree on anything.鈥� He
expects that rough and ready schemata will become standards by default simply
because people will start using them.
The benefits of RDF will come not only from smarter searching, but also from
making it easier to transfer and pool data. Using the Dublin Core, for example,
it will be possible to amalgamate bibliographies from different institutions,
and so create a kind of virtual, global library catalogue.
Even where no formal schema has been drawn up, XML can still help information
interchange. Take two companies that hold similar information in their
databases, but use different programs running on incompatible computers and use
different names for their database fields鈥攐ne uses SecondName, for
example, while the other uses Surname. If these databases are converted to XML,
then the fields become pairs of tags and the data within the fields are placed
between the tags. So the first company鈥檚 tags become
and the second firm鈥檚
simple text-processing program to translate one set of tags into the other.
One area that is likely to be transformed by XML鈥檚 interchange capabilities
is e-commerce. In particular, electronic data interchange (EDI)鈥攁n attempt
to define standard ways for companies to exchange orders
electronically鈥攎ay well be re-energised. 鈥淢any of us feel that XML is
the best way to move EDI on to the Internet,鈥� says Patrick Drummond, a member of
the EDI working group of the American forum CommerceNet. In the past, companies
have been loath to switch to EDI because it needs expensive software. But XML
programs are likely to be freeware, shareware or low cost.
It鈥檚 not just commerce that will benefit, however. 鈥淚 believe that XML will
have a breakthrough impact on electronic record-keeping in healthcare,鈥� says Tom
Lincoln, research professor of medical informatics at the University of Illinois
at Chicago. The ability to pool medical information from many hospitals and
search for, say, patterns of disease or successful treatments among the records
of tens or even hundreds of thousands of people could transform
epidemiology.
One other intriguing aspect of XML is that it鈥檚 not confined to words and
numbers. With the right tags, it can be used to convey just about anything,
including mathematical, musical and chemical symbols. Already, this has led to
XML applications such as the
Mathematics Markup Language (http://www.w3c.org/Math/),
Music Markup Language (http://www.tcf.nl/trends/trends6-en.html),
and the Chemical Markup Language (http://www.venus.co.uk/omf/cml/ intro.html).
The latter, CML, can manage any existing molecular information on the Web,
says its creator Peter Murray-Rust, director of the Virtual School of Molecular
Sciences at Nottingham University. One of the advantages of XML is that it is
designed to support different disciplines working together, he continues: 鈥淪o
it鈥檚 very straightforward to mix text, maths and chemistry in the same
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Automatic access
Perhaps the most astonishing feature of CML and other XML applications is
that it is possible to write software that will select data held between pairs
of tags and then manipulate them automatically. This makes the data not just
searchable but manipulable in ways that are impossible today, says Murray-Rust.
You could, say, write a program that grabbed some numbers from an XML chemistry
paper, modified them in some way and sent the results to a computer-controlled
chemical production process鈥攁ll without human intervention.
Radical it may be, but not everyone is so sure that XML will bring unalloyed
benefits. Tim Brady, vice-president of production at Yahoo, the Web鈥檚 most
popular destination, is unequivocal about its negative effects. 鈥淴ML will make
it easier for business to spam search engines,鈥� he says. That is, XML will allow
the unscrupulous to add spurious metadata that will put their Web pages higher
up in search lists, or even in completely inappropriate ones. Still, as Lassila
says, 鈥渁ny technology can be used for fraud and deception鈥�.
More serious is a warning sounded by Mark Pesce, co-inventor of the Virtual
Reality Modelling Language (VRML) used for creating three-dimensional worlds.
His fear is that if different groups of Web page designers stick to their own
tags it could lead to 鈥淏alkanisation鈥� of the Web. Lassila admits this is a
frightening idea but argues that RDF is designed specifically to stop it
happening.
And Bray thinks the notion of the Web splitting up is nonsense. 鈥淭here鈥檚 no
point in creating my own tags unless I want other people to use them,鈥� he says.
鈥淢y tags will need to be included in a stylesheet and offer some software that
does something interesting.鈥� These constraints will make it difficult to get
tags widely accepted.
Like Bray, most people are upbeat about XML. Even those traditional rivals
Microsoft and Netscape are united in supporting the XML revolution. Bartlett at
ArborText has no doubts about what鈥檚 going on. 鈥淴ML,鈥� he says, 鈥渨ill prove to be
one of the top ten technological innovations of the first century of
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