The GRID, the Semantic Web and Web Services: Balancing wishful thinking with reality
Henry S. Thompson
British Computer Society, Edinburgh, 2005-10-26
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
My quick summary of Web Services:
Loosely-coupleddistributed applications
Three key aspects:
Messages-XMLP (ex-SOAP), XML Schema
Definition-WSDL: XML->XML function signatures
Discovery-UDDI (CORBA, oops)
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
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.
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?
Meaning is at the Core
Both SW and WS depend crucially on moving beyond syntax
XML as such is just ASCII for the 21st 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 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
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
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
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) 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
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
The Semantic Web Today
1 ½ of the four first requirements for metadata I mentioned earlier:
RDF Model and Syntax gives us recognisable metadata
First RDF Schema, now OWL, give us mechanisms for defining shared vocabularies, and we have a few
Realism has overtaken the dream
Focus on information interchange within individual companies or (in a few cases) industry groups
Usable tools and products beginning to emerge
The Semantic Web Tomorrow
Starting serious work on Queries, Rules, Logic and Trust
The big open question: will the parallel with the OFW hold up?
The OFW succeeded because of human detection and exploitation of separately developed web resources.
Will automatic detection and exploitation of separately developed knowledge resources on the SW actually happen?
Will separate efforts use common ontologies?
If
they do, will that be enough to allow reliable identification of co-referents?
Or will the SW turn to probably nearly correct results by exploiting statistical mechanisms, as much of the rest of AI has done?
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
Practical implications
Don't give up good old-fashioned requirements analysis
Consider Semantic ... for interfacing in tightly constrained circumstances
But don't hold your breath waiting for the Semantic Grid
or any other decentralised discovery-based use of Semantic Web technologies
This is just reduction to a previously unsolved problem
Don't confuse modelling your data with encoding it:
Look at RDF plus OWL as an alternative to E-R or UML for modelling your data
Use XML Schema to define XML encodings of your data for transmision and interchange
Take advantage of the leverage the industrial community will give the Web Services story
But be very careful about IPR
Getting involved -- W3C Semantic Web work today
Standardization work is underway in
Query
and
Best Practices
.
RDF Data Access Working Group
Gather requirements and define an HTTP and/or SOAP-based protocol for selecting instances of subgraphs from an RDF graph
The goal of this work is to help make it as easy to 'join' data on the Web as it is to merge tables in a local relational database.
Use Cases and Requirements
SPARQL Query Language
, and
SPARQL Protocol
Working Drafts available
Best Practives and Deployment
Provide guidance, in the form of documents and demonstrators, for developers of Semantic Web applications.
Develop consensus best practices on ontology engineering guidelines, vocabulary development, educational material and demo applications.
Support initiatives for transforming selected high-visibility ontologies and thesaurii to OWL and RDF.
Planning Workshops
Life Sciences
, October 27-28 2004, Cambridge MA
Rules
Workshop, 27-28 April 2005, Washington DC
Semantic Web Services
, June 9-10, 2005, Innsbruck, Austria