1 csit600f: introduction to semantic web dickson k.w. chiu phd, smieee text: antoniou & van...

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CSIT600f: Introduction to Semantic Web

Dickson K.W. ChiuPhD, SMIEEE

Text: Antoniou & van Harmelen: A Semantic Web Primer

Ref: Ivan Herman: Tutorial on Semantic Web Technology

Dickson Chiu 2006 CSIT600b s1-2

Towards a Semantic Web

WWW is an impressive success: amount of available information (> 1 Giga-page) number of human users (> 200 Mega-user)

The current Web represents information using natural language (English, Hungarian, Chinese,…) graphics, multimedia, page layout

Humans can process this easily can deduce facts from partial information can create mental associations are used to various sensory information

(well, sort of… people with disabilities may have serious problems on the Web with rich media!)


Need for understanding Web info

Tasks often require to combine data on the Web: hotel and travel infos may come from different

sites searches in different digital libraries etc.

Again, humans combine these information easily even if different terminologies are used!


However…

However: machines are ignorant! partial information is unusable difficult to make sense from, e.g., an image drawing analogies automatically is difficult difficult to combine information

is <foo:creator> same as <bar:author>?

how to combine different XML hierarchies?

…


Example: Searching

The best-known example… Google et al. are great, but there are too

many false hits adding descriptions to resources should

improve this


Where we are Today: the Syntactic Web

[Hendler & Miller 02]


The Syntactic Web is… A hypermedia, a digital library

A library of documents called (web pages) interconnected by a hypermedia of links

A database, an application platform A common portal to applications accessible through web

pages, and presenting their results as web pages A platform for multimedia

BBC Radio 4 anywhere in the world! Peer-to-peer sharing (BT, edonkey, PPLive, …)

A naming scheme Unique identity for those documents

A place where computers do the presentation (easy) and people do the linking and interpreting (hard).

Why not get computers to do more of the hard work?


Hard using the Syntactic Web… Finding the image of something

Find pictures that contain red birds with blue background Complex queries involving background knowledge

Find information about “animals that use sonar but are not either bats or dolphins”

Locating information in data repositories Travel enquiries Prices of goods and services Results of human genome experiments

Finding and using “web services” Visualise surface interactions between two proteins

Delegating complex tasks to web “agents” Book me a holiday next weekend somewhere warm, not too far

away, and where they speak French or English


What is the Problem?

Consider a typical web page:

Markup comprise rendering

information (e.g., font size and colour)

Hyper-links to related content

Semantic content is accessible to humans but not (easily) to computers…


What information can we see…WWW2002The eleventh international world wide web conferenceSheraton waikiki hotelHonolulu, hawaii, USA7-11 may 20021 location 5 days learn interactRegistered participants coming fromaustralia, canada, chile denmark, france, germany, ghana, hong

kong, india, ireland, italy, japan, malta, new zealand, the netherlands, norway, singapore, switzerland, the united kingdom, the united states, vietnam, zaire

Register nowOn the 7th May Honolulu will provide the backdrop of the eleventh

international world wide web conference. This prestigious event …

Speakers confirmedTim berners-lee Tim is the well known inventor of the Web, …Ian FosterIan is the pioneer of the Grid, the next generation internet …


Information a machine may see…

…

…

…


Solution: XML markup with “meaningful” tags?

<name> </name><location>

</location>…

How about…<conf> </conf>

<place>

</place>

Then how about…< 会议 >

</ 会议 >

< 地点 >

</ 地点 >


What Is Needed?

A resource should provide information about itself also called “metadata” metadata should be in a machine

processable format agents should be able to “reason” about

(meta)data metadata vocabularies should be defined


What Is Needed (Technically)?

To make metadata machine processable, we need: unambiguous names for resources (URIs) a common data model for expressing

metadata (RDF) and ways to access the metadata on the Web

common vocabularies (Ontologies) The “Semantic Web” is a metadata

based infrastructure for reasoning on the Web

It extends the current Web (and does not replace it)


Adding “Semantics” External agreement on meaning of annotations

E.g., Dublin Core (http://dublincore.org/) Agree on the meaning of a set of annotation tags

Problems with this approach Inflexible Limited number of things can be expressed

Use Ontologies to specify meaning of annotations Ontologies provide a vocabulary of terms New terms can be formed by combining existing ones Meaning (semantics) of such terms is formally specified Can also specify relationships between terms in

multiple ontologies


History of the Semantic Web Web was “invented” by Tim Berners-Lee (amongst others), a

physicist working at CERN TBL’s original vision of the Web was much more ambitious

than the reality of the existing (syntactic) Web:

TBL (and others) have since been working towards realising this vision, which has become known as the Semantic Web

E.g., article in May 2001 issue of Scientific American…

“... a goal of the Web was that, if the interaction between person and hypertext could be so intuitive that the machine-readable information space gave an accurate representation of the state of people's thoughts, interactions, and work patterns, then machine analysis could become a very powerful management tool, seeing patterns in our work and facilitating our working together through the typical problems which beset the management of large organizations.”


Berner-Lee’s Architecture

Data Exchange

Semantics+reasoning

Relational Data?

?

???

???

???

• Relationship between layers is not clear• OWL DL extends “DL subset” of RDF


A Spectrum of Ontology

Catalog/ID

GeneralLogical

constraints

Terms/glossary

Thesauri“narrower

term”relation

Formalis-a

Frames(properties)

Informalis-a

Formalinstance

Value Restrs.

Disjointness, Inverse, part-

of…


Ontology in Philosophy - a philosophical discipline—a branch of philosophy that deals with the nature and the organization of reality

Science of Being (Aristotle, Metaphysics, IV, 1) studies being or existence as well as the basic

categories thereof trying to find out what entities and what types of

entities exist has strong implications for the conceptions of

reality.

Ontology: Origins and History


Ontology in Linguistics

“Tank“

ReferentFormStands for

Relates toactivates

Concept

[Ogden, Richards, 1923]?


An ontology is an engineering artifact [Neches91]: defines basic terms and relations comprising the

vocabulary of a topic area the rules for combining terms and relations to define

extensions to the vocabulary “An explicit specification of a conceptualization”

[Gruber93] Formal specification of a shared conceptualization

(of a certain domain) [Borst 97]: Shared understanding of a domain of interest Formal and machine manipulable model of a domain of

interest

Ontology in Computer Science


Structure of an OntologyOntologies typically have two distinct components:1. Names for important concepts in the domain

Elephant is a concept whose members are a kind of animal Herbivore is a concept whose members are exactly those

animals who eat only plants or parts of plants Adult_Elephant is a concept whose members are exactly

those elephants whose age is greater than 20 years

2. Background knowledge/constraints on the domain Adult_Elephants weigh at least 2,000 kg All Elephants are either African_Elephants or

Indian_Elephants No individual can be both a Herbivore and a Carnivore


Ontology Elements Concepts (classes) + their hierarchy Concept properties (slots / attributes) Property restrictions (type, cardinality, domain,

etc.) Relations between concepts (disjoint, equality, etc.) Instances

E-R diagram / UML diagram ??? Note: “Property” “Slot” “Relation” “Relationtype”

“Attribute” Semantic link type”


A Semantic Web — First Steps

Extend existing rendering markup with semantic markup Metadata annotations that describe content/function of web

accessible resources Use Ontologies to provide vocabulary for annotations

“Formal specification” is accessible to machines A prerequisite is a standard web ontology language

Need to agree common syntax before we can share semantics Syntactic web based on standards such as HTTP and HTML

Make web resources more accessible to automated processes


More Example: Automatic Assistant

Your own personal (digital) automatic assistant knows about your preferences builds up knowledge base using your past can combine the local knowledge with remote services:

hotel reservations, airline preferences dietary requirements medical conditions calendaring etc

It communicates with remote information (i.e., on the Web!)


Example: Database Integration

Databases are very different in structure, in content Lots of applications require managing several

databases after company mergers combination of administrative data for e-Government biochemical, genetic, pharmaceutical research etc.

Most of these data are now on the Web The semantics of the data(bases) should be known

how this semantics is mapped on internal structures is immaterial


Example: Digital Libraries

It is a bit like the search example It means catalogs on the Web

librarians have known how to do that for centuries

goal is to have this on the Web, World-wide extend it to multimedia data, too

But it is more: software agents should also be librarians! help you in finding the right publications


Example: Semantics of Web Services

Web services technology is great But if services are ubiquitous, searching issue

comes up, for example: “find me the most elegant Schrödinger equation solver” what does it mean to be

“elegant”? “most elegant”?

mathematicians ask these questions all the time… It is necessary to characterize the service

not only in terms of input and output parameters… …but also in terms of its semantics


How Simple Ontologies Help

not as costly to build and potentially more importantly, many are available provide a controlled vocabulary website organization and navigation support support expectation setting (e.g. user

interface) “umbrella” structures from which to extend

content (e.g., UNSPSC) searching support sense disambiguation support (e.g., terms

belong to different categories) Deborah McGuinness. Ontologies Come of Age. The Semantic Web: Why, What and How, MIT Press, 2001. (MS-Word)


How Structured Ontologies Help

more structure => more power consistency checking completion (of unspecified attributes and

relations) interoperability support validation and verification testing or even

encode entire test suites structured, comparative, and customized

search “intelligence” in application, e.g., system

configuration support


Benefits of Semantic Web

Communication between people Interoperability between software agents Reuse of domain knowledge Make domain knowledge explicit Analyze domain knowledge


The Semantic Web is Not “ Artificial Intelligence on the Web”

although it uses elements of logic… … it is much more down-to-Earth (we will see later) it is all about properly representing and characterizing metadata of course: AI systems may use the metadata of the SW

but it is a layer way above it

“A purely academic research topic” SW is out of the university labs now lots of applications exist already (see examples later) big players of the industry use it (Sun, Adobe, HP, IBM,…) of course, much is still be done!

Building an ontology is not a goal in itself

1 csit600f: introduction to semantic web dickson k.w. chiu phd, smieee text: antoniou & van...

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dickson chiu 2006csit600b