Web Services and the Semantic Web:

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Oct 20, 2013 (3 years and 8 months ago)

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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

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

2

Web Services

Semantic Web


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

3

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 (CORBA, oops)

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

4

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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

5

The Origins of the Semantic Web


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?


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

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

6

First Requirements for Metadata


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?

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

7

Meaning is at the Core


Both SW and WS depend crucially on moving
beyond syntax


XML as such is just ASCII for the 21
st

century


Web
-
appropriate linearisation


for tree
-
structured documents with internal links


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

8

Web Services and the GRID


Services and resources are not electrons


And computers 'looking' for 'service providers' are not the
same as human beings shopping on the web


So the metaphors underlying both WS and the GRID
can be very misleading


Negotiation between producers and consumers is the
key


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

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

9

Those Who do not Study History


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

The History of the Knowledge
Representation Problem


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

10

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

11

The Missing Inference Engine


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


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:


Use (something isomorphic to) 1
st
-
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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

12

How is a KR System like a Piano?


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


CYC was the last and biggest failure


and the least excusable


CYC was the grandparent of RDF



So RDF has some ground to make up

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

13

The Semantic Web Today


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

14

The Semantic Web Tomorrow


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

15

The reality of Web Services


Forget the headline stuff (with all due respect to our
sponsors)


Cars negotiating with petrol stations


Agents choosing a specialist based on available appointment
slots


The focus in practice is on exploiting the move to
asynchronous distributed applications


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

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

16

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


But be
very

careful about IPR

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

17

A Bewildering Range of Choice


"The wonderful thing about standards is that


there 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 (?)

Web Services

Semantic Web

Henry S. Thompson

GGF, Edinburgh, 2002
-
07
-
23

18

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