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FEATURE STORY 67
to sexually explicit material online, and Web researchers had
responded with a system of computer-readable labels iden-
tifying such content. The labels could be applied either by
Web publishers or by ratings boards. Software could then use
these labels to lter out objectionable content, if desired.
Miller, among others, saw larger possibilities. Why, he
asked, limit the descriptive information associated with
Web pages to their suitability for minors? If Web content
was going to be labeled, why not use the same infrastruc-
ture to classify other information, like the price, subject, or
title of a book for sale online? That kind of general-purpose
metadata---which, unlike XML, would be consistent across
sites---would be a boon to people, or computers, looking for
things on the Web.
This idea resonated with other Web researchers, and in
the late 1990s it began to bear fruit. Its rst major result was
the Resource Description Framework (RDF), a new system
for locating and describing information whose speci ca-
tions were published as a complete W3C recommendation
in 1999. But over time, proponents of the idea became more
ambitious and began looking to the arti cial-intelligence
community for ways to help computers independently
understand and navigate through this web of metadata.
Since 1998, researchers at W3C, led by Berners-Lee, had
been discussing the idea of a "semantic" Web, which not only
would provide a way to classify individual bits of online data
such as pictures, text, or database entries but would de ne
relationships between classi cation categories as well. Dic-
tionaries and thesaur uses called "ontologies" would translate
between di erent ways of describing the same types of data,
such as "post code" and "zip code." All this would help com-
puters start to interpret Web content more e ciently.
In this vision, the Web would take on aspects of a data-
base, or a web of databases. Databases are good at providing
simple answers to queries because their software understands
the context of each entry. "One Main Street" is understood
as an address, not just random text. De ning the context of
online data just as clearly---labeling a cat as an animal, and a
veterinarian as an animal doctor, for example---could result
in a Web that computers could browse and understand much
as humans do, researchers hoped.
To go back to the Web-as-highway metaphor, this might
be analogous to creating detailed road signs that cars them-
selves could understand and upon which they could act. The
signs might point out routes, describe road and tra c condi-
tions, and o er detailed information about destinations. A
car able to understand the signs could navigate e ciently to
its destination, with minimal inter vention by the driver.
In articles and talks, Ber ners-Lee and others began
describing a future in which software agents would simi-
larly skip across this "web of data," understand Web pages
metadata content, and complete tasks that take humans
hours today. Say you d had some lingering back pain: a
program might determine a specialist s availability, check
an insurance site s database for in-plan status, consult your
calendar, and schedule an appointment. Another program
might look up restaurant reviews, check a map database,
cross-reference open table times with your calendar, and
make a dinner reservation.
At the beginning of 2001, the e ort to realize this vision
became o cial. The W3C tapped Miller to head up a new
Semantic Web initiative, unveiled at a conference early that
year in Hong Kong. Miller couldn t be there in person; his
wife was in labor with their rst child, back in Dublin.
Miller saw it as a double birthday.
Standards and Critics
The next years weren t easy. Miller quickly had to become
researcher, diplomat, and evangelist. The e ort to build
the Semantic Web has been well publicized, and Berners-
Lee s name in particular has lent its success an air of near-
inevitability. But its visibility has also made it the target of
frequent, and often harsh, criticism.
Some argue that it s unrealistic to expect busy people and
businesses to create enough metadata to make the Seman-
tic Web work. The simple tagging used in Web 2.0 applica-
tions lets users spontaneously invent their own descriptions,
which may or may not relate to anything else. Semantic Web
systems require a more complicated infrastructure, in which
developers order terms according to their conceptual relation-
ships to one another and---like Dewey with his books--- t data
into the resulting schema. Creating and maintaining these
schemas, or even adapting preëxisting ones, is no trivial task.
Coding a database or website with metadata in the language
of a schema can itself be painstaking work. But the solution
to this problem may simply be better tools for creating meta-
data, like the blog and social-networking sites that have made
building personal websites easy. "A lot of Semantic Web
researchers have realized this disconnect and are investing
in more human interfaces," says David Huynh, an MIT stu-
dent who has helped create several such tools.
This idea had been dropped in favor of the simple, one-size-fits-all
hyperlink. But Berners-Lee didn't give it up altogether, and the idea of
connecting data with links that meant something retained its appeal.
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