A Vigil on the Semantic Web

Bruce SpencerNRC-IIT Fredericton

Aug 22, 2001

Abstract Much of the AI community that met at IJCAI in August 2001 was discussing the

"Semantic Web", a proposal by the inventor of the web, Tim Berners-Lee, and others to adding meaning to terms for items found on the web, with a view to making the web interactions more accurate and more easily automated. Several US and European projects are concerned with creating and using taxonomies of terms in web page design and retrieval, and are supported by W3C and DARPA. The DAML+OIL language, a joint US-European project, proposes to add Resource Description Framework (RDF) to Extensible Markup Language (XML), tagging web content with meta-tags containing links to ontologies, as well as facts and rules that describe the intended use of the content. This draws from a quarter century of work in knowledge representation and reasoning systems by the artificial intelligence community.

In this talk I will explain the goals and achievements of the Semantic Web effort to date, and point out (some of) the remaining hurdles, and assuming that they are cleared, what these researchers expect to emerge. Interoperation among applications that exchange machine-understandable information will allow automated processing of web resources, and this has many applications in ecommerce. I will close with a suggestion how the IIT-Fredericton's Security/Privacy, Multi-Agent and "One Web" thrusts can be aligned with these international efforts.

Five main points

• Tim Berners-Lee’s vision–web information should be machine

understandable• Taxonomies of words shared within web

communities– no single ontology

• RDF: meta-tags link XML tags to their roles• US and European buy-in–Where’s Canada

• Aligns with IIT Fredericton’s thrusts–multi-agent, security, OneWeb, voice

Identifying Resources

• URL/URI– Uniform resource locator / indicator– Information sources, goods and services– financial instruments• money, options, investments, stocks, etc.

• “Where do you want to go today?” – becomes “What do you want to find?”

Ontology• Branch of metaphysics dealing with the

philosophical theory of reality• Tarski: individuals, relationships and roles• “A common vocabulary and agreed-upon

meanings to describe a subject domain”–What real-world objects do my tags refer to? –How are these objects related?

• Communication requires shared terms– others can join in

What your computer sees in HTML<b>Joe’s Computer Store</b><br> 365 Yearly Drive

What your computer sees in XML<location><address><name>Joe’s Computer Store</name><address> 365 Yearly Drive</address></location>

Presentation information

Content description

(ambiguous)

What a computer could understand

<mail:address xmlns:mail=“http://www.canadapost.ca”><mail:name>Joe’s Computer Store </mail:name><mail:street> 365 Yearly Drive </mail:street></mail:address>

• www.canadapost.ca could define address, name, street, …

• Search engines could then identify mail addresses• Consider shopbots being able to find – price, quantity, feature, model number, supplier, serial

number, acquisition date• Assumes that namespaces will be used consistently

Semantic Web

• An agent-enabled resource• “information in machine-readable form, creating

a revolution in new applications, environments and B2B commerce”

• Launched Feb 9, 2001• DAML: DARPA Agent Markup Language–US Gov funding to define languages, tools– 16 project teams

• OIL is Ontology Inference Layer–DAML+OIL is joint DARPA-EU

• KR a natural choice

Tim Berners- Lee’s Semantic Web

RDF Resource Description Framework

• Beginning of Knowledge Representation influence on Web

• Akin to Frames, Entity/Relationship diagrams, or Object/Attribute/Value triples

RDF Example

<rdf:ProductSpecs> about=“http://www.lemoncomputers.ca/model_2300”>

<specs:colour>yellow</specs:colour><specs:size>medium</specs:size></rdf:ProductSpecs>

model_2300

size

medium

colour

yellow

RDF Class Hierarchy

• All lemon laptops get packed in cardboard boxes

• Allows one to customize existing taxonomies– Example: palmtop

computers still get packed in boxes

lemon_palmtop_20000

is_a

model_2300

size

medium

colour

yellow

Tim Berners- Lee’s Semantic Web

Ontology Layer

• Widens interoperability and interconversion– knowledge representation

• More meta-information–Which attributes are transitive, symmetric–Which relations between individuals are 1-1,

1-many, many-many• Communities exist–DL, OIL, SHOE (Hendler)–New W3C working group

Transitive, Subrole example

• One wants to ask about modes of transportation from Sydney to Fredericton

• “connected by Acadian Lines bus” is a role in a Nova Scotia taxonomy

• “connected by SMT bus” from New Brunswick• Both are subroles of “connected”• “connected” is transitive• Note that ontologies can be combined at runtime

Combining Rich Ontologies• Only these facts are

explicit– in separate

ontologies• “Connected by bus” – is superset– is symmetric and

transitive• Route from Sydney to

Fredericton is inferred

Connected by Acadian Lines

Connected by Acadian Lines

Sydney

Truro

Amherst

Fredericton

Connected by SMT Lines

Sussex

Connected by SMT Lines

Amherst

Tim Berners- Lee’s Semantic Web

Logic Layer

• Clausal logic encoded in XML–RuleML, IBM CommonRules

• Special cases of first-order logic–Horn Clauses for if-then type reasoning and

integrity constraints• Standard inference rules based on Resolution– Various implementations: SQL, KIF, SLD

(Prolog), XSB– I’ve developed reasoning tools in Java.

• Modus operandi: build tractable reasoning systems– trade some expressiveness

Logic Architecture Example• Contracting parties integrate e-businesses via rules

BusinessRules

BusinessRules

OPS5Prolog

Contract Rules Interchange

Seller E-Storefront Buyer’s ShopBot

Negotiation via rules

<usualPrice> price(per-unit, ?PO, $60)

purchaseOrder(?PO, supplierCo, ?AnyBuyer) shippingDate(?PO, ?D) (?D 24April2001).

<volumeDiscountPrice> price(per-unit, ?PO, $55)

purchaseOrder(?PO, supplierCo, ?AnyBuyer) quantityOrdered(?PO, ?Q) (?Q 1000) shippingDate(?PO, ?D) (?D 24April2001).

overrides(volumeDiscount, usualPrice).

Eventual Goal of these Efforts

• Agents locate goods, services– use namespaces, ontologies– unambiguous– business rules– expressive language but reasoning tractable– combine from various sources

• Gives rise to needs trust, privacy and security– e.g. semantic web project to determine

eligibility of patients for a clinical trial

Aligning with IIT’s identified thrusts

• Privacy– Tim Berners-Lee’s “Web of Trust” digital

signatures• Multi Agents Systems• One Web– high degree of interoperability– shared ontologies need to be multilingual and

multicultural

What could IIT-Fredericton do?

• W3C working group on Semantic web ontologoes announced Aug 13– request for participants–We need to be poised to adopt emerging

standards.• Build prototypes–with an industrial partner• resource location (goods and services)• procurement• markup-for-free• match ontologies

What could IIT-Fredericton do?

• International partners: – DFKI (Germany) Harold Boley– Rutherford Appleton (UK) Theo Dimitrakos

Easy reading“Agents and the Semantic Web” IEEE Intelligent Systems

Journal March/April 2001, James Hendler. “The Semantic Web” Scientific American, June 2001, Tim

Berners-Lee, James Hendler, Ora Lassila.