Transcript Web services and the Semantic Web: Separating Hype from Reality

Web Services and the Semantic Web:
Separating Hype from Reality
Henry S. Thompson
HCRC Language Technology Group
Division of Informatics
University of Edinburgh,
Markup Technology Ltd.
and
World Wide Web Consortium
© 2000 Henry S. Thompson
Web Services—Semantic Web
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Web Services is the name for a marketing
initiative
 The
technology has been scrambling to catch up
and provide some grounding for the phrase ever
since it was invented

The Semantic Web is the name for a vision of
the future
 Originally
Tim Berners-Lee's attempt to answer the
question: What is the full potential of the (World
Wide) Web?

They have a common dependency
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GGF, Edinburgh, 2002-07-23
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Web Services
You've heard a lot about Web Services in the
preceding talk
 My quick summary:

 Loosely-coupled

distributed applications
Three key aspects:
 Messages—XMLP
(ex-SOAP), XML Schema
 Definition—WSDL: XML->XML function
signatures
– Queue shameless plug for Markup Technology 
 Discovery—UDDI
Web Services—Semantic Web
(CORBA, oops)
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Semantic Web
Just as XML is SGML specialised for the
WWW
 You can think about the Semantic Web as UML
for the WWW
 Initially (RDF) just a simple relation-triple
model of assertions about resources

 Serialised
as XML
 With a few bells and whistles for collections and
reflection

Starting to grow
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The Origins of the Semantic Web
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The information retrieval crisis beginning in the late
1990s led to a widespread interest in what has come to
be called metadata.
What is metadata?

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It's just data.
But it's data about other data
Data intended for machine consumption
What could metadata do for us?


Give search engines something to work with (relational
triples) that is designed for their needs.
Give us all a place to record what a document, or any other
resource, is for or about.
Web Services—Semantic Web
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First Requirements for Metadata
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What would we need to make this work?
A
standard syntax, so metadata can be recognised
as such;
 One or more standard vocabularies, so search
engines, producers and consumers all speak the
same language;
 Lots of resources with metadata attached;
 Attribution and trust
– Is this resource really about Pamela Anderson?
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Meaning is at the Core

Both SW and WS depend crucially on moving
beyond syntax
 XML as such is just ASCII for the 21st
– Web-appropriate linearisation
– for tree-structured documents with internal links
century
– and tree-structured documents are a pretty good transfer
syntax for just about anything
 What
prospects for moving beyond syntax to
semantics?
– The Semantic Web is committed by its very name
– Web Services can't succeed without it
– And this is where relevance to the GRID kicks in
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Web Services and the GRID
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Services and resources are not electrons

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So the metaphors underlying both WS and the GRID
can be very misleading
Negotiation between producers and consumers is the
key

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

And computers 'looking' for 'service providers' are not the
same as human beings shopping on the web
If you can’t describe what you want, you can’t have it
If you can’t describe what you’ve got, no-one will use it
If you can’t dicker, you’ll always lose
These observations apply equally well to Web Services
and the GRID
Web Services—Semantic Web
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Henry S. Thompson
Those Who do not Study History
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are doomed to repeat it
 The history of AI is full of examples of two
weaknesses:

 Over-promising
by insiders
– 'AI Winter'; Intelligent Agents
 Over-optimism

by outsiders
25 years ago Ed Feigenbaum described Terry
Winograd’s work as “a breakthrough in
enthusiasm”
I
worry that WS and SW, in their reliance on
effective computational semantics, are vulnerable to
the same criticism
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The History of the Knowledge
Representation Problem
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The representation and exploitation of knowledge has
been the ultimate grand challenge for Artificial
Intelligence since its inception
Our own human intelligence has sometimes been a
real handicap

It's too easy to look at a screenshot and see how much
knowledge is captured
(#$and
(#$isa ?x #$Person)
(#$feelsEmotion ?x #$Fear #$High))

Designing apparently expressive notations is easy

Making them do actual work is much harder
Web Services—Semantic Web
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The Missing Inference Engine
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What we learned in 1978–79 was that designing an
approach to KR without first designing an inference
engine was a waste of time
Actually worse than a waste of time
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Because you could invest a lot of work in representing stuff
And still end up with nothing to show for it
So we were left with an embarrassing tradeoff:
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Use (something isomorphic to) 1st-order predicate logic, and
get a variety of pretty well-understood inference engines
Use something more user-friendly and expressive, but be
unable to exploit it
This tradeoff is still with us today
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How is a KR System like a Piano?
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The title of a 1980 Special Issue of SIGART
 The
end of the beginning, with hindsight
KRL, Semantic Nets, KL-ONE, . . .
 Where are they now?

 Learned
the lesson of the missing engine the hard
way
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CYC was the last and biggest failure
 and
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the least excusable
CYC was the grandparent of RDF
 So
RDF has some ground to make up
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The Semantic Web Today
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1 ½ of the four first requirements for metadata
I mentioned earlier:
 RDF
Model and Syntax gives us recognisable
metadata
 RDF Schemas gives us a mechanism for defining
shared vocabularies, and we have a few
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The Semantic Web Tomorrow
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Reworking the syntax and cleaning up the
model
 Extending the definition mechanism
(DAML+OIL –> Web Ontology Language)
 Starting serious work on Rule, Logic and Trust

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The reality of Web Services

Forget the headline stuff (with all due respect to our
sponsors)
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The focus in practice is on exploiting the move to
asynchronous distributed applications
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Cars negotiating with petrol stations
Agents choosing a specialist based on available appointment
slots
Within the enterprise, not between enterprises
Using pre-negotiated vocabularies, and little or no discovery
IT-intensive enterprises see Web Services primarily as
a way to reduce their EAI/middleware bills
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Implications for the GRID

Don't hold your breath waiting for the
Semantic Grid
 Reduction
to a previously unsolved problem
Don't confuse modelling your data with
encoding it
 Look at RDF or WebOnt as an alternative to
E-R or UML for modelling your data
 Use XML Schema to define your data encoding
 Take advantage of the leverage the industrial
community will give the Web Services story
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 But
be very careful about IPR
Web Services—Semantic Web
GGF, Edinburgh, 2002-07-23
Henry S. Thompson
A Bewildering Range of Choice

"The wonderful thing about standards is that
 there
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are so many to choose from"
Unfortunately true today for standards
organisations as well
 World
Wide Web Consortium (W3C)
– HTML, XML and friends
 Internet
Engineering Task Force (IETF)
– HTTP, TCP/IP, DNS
 Organization
for the Advancement of Structured
Information Standards (OASIS)
– ebXML, Web Services Security (?)
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GGF, Edinburgh, 2002-07-23
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Choice, cont'd

More standards bodies
 Web
Services Interoperability Organisation (WS-I)
– ??
 International
Standards Organisation (ISO)
– Topic Maps

Why has this happened?
 Different
time scales
 Different requirements for review and proof of
interoperability
 Different approaches to IPR
Web Services—Semantic Web
GGF, Edinburgh, 2002-07-23
Henry S. Thompson