The W3C’s Semantic Web

Kyle Mosack

The Semantic Web"The Semantic Web is not a separate Web

but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation." It is a source to retrieve information from the web (using the web spiders from RDF files) and access the data through Semantic Web Agents or Semantic Web Services.”

Source: "The Semantic Web" by Tim Berners-Lee, James Hendler, and Ora Lassila, Scientific American, 2001

What It Could BeMachine Readable Data View

◦ Having data on web be defined an linked in a way that can be read by machine for automation, integration, and re-use across different applications

Intelligent Agent View◦ Agents retrieve and manipulate pertinent information

Distributed Data View◦ Provide sufficient flexibility to be able to represent all

databases and logic rules to link them togetherAutomated Infrastructure View

◦ Current web lacks an easy automation framework

What it Could BeServant of Humanity View

◦ Enable Web applications to automatically collect , integrate, and process information and interoperate with other applications

Better Annotation View◦ Annotations expressed in a machine processable

form and linked togetherImproved Searching View

◦ Access Web content by concepts instead of keywords

Web Services View◦ Expand services from existing web by automating

services with Web agents

Semantic Web Layer Cake

Semantic Web Layer Cake

Readable Description FrameworkDesigned for specific data about

specific subjectsCan represent Data and

MetadataMoves proprietary data to a form

computers can analyzeRecommendation from W3C for

Semantic Web

RDFTo be successful RDF must be

able to

◦Describe most kinds of data that will be available

◦Describe structural design of data sets

◦Describe relationships between bits of data

RDFCreates a data model with

triplets◦Subject, predicate (property), object

(property value)◦These are statements about

resources Identified by URI

◦Easily convertible◦Not limited by predefined database

values Flexible

RDF Graph with Anonymous Nodes

RDF ApplicationsMozilla

◦Uses XUL (extensible user interface language)◦Uses RDF as a source for listings and other control

information that defines which XUL files to use for specific XUL interfaces

RSS (Really Simple Syndication)◦Helps spread summaries of personal blogs cheaply

and easily◦Uses RDF’s XML exchange format◦One of the few RDF applications that is distributed

over the Web rather than being used locally, unlike Mozilla application

Can be seen as an early, maybe primitive, Semantic Web Application

RDF ApplicationsRDF for annotations: Annotea

◦Experimental scheme by W3C for annotating Web pages

Bibliographic meta data: Dublin Core◦Provides practical standard terms applicable

to nearly any published workWebscripter: Fusing Information

◦DAML (DARPA Agent Markup Language)◦Ability to make up web pages so that

information about the page can be extracted in a uniform way and combined with other web pages

RDF and the Semantic Web

Abilities beyond conventional database◦Combine data with different data sets that don’t

follow the same data models◦Add data that doesn’t fit the table structures◦Exchange data with any other application that can

handle RDF◦Use an RDF processor that can do logical reasoning

to discover unstated relationships◦Use someone else’s ontology to learn more about

own data◦Add statements about publications and references

that have been defined somewhere else on the Web◦Do all these things using well defined standards, so

wide range of applications can process the data

RDF – Potential ProblemsMany stem from nature of the

Web◦Incomplete information◦Contradictory or unreliable

informationFull first order logic requires an

ability to generate general statements about the whole table

No way to negate statementsMay not be powerful enough

OntologyStudy of existence or beingThe kinds of things that can be

talked about in a system or context

Provides the means to classify these properties◦Name and label them

Kinds of organization include◦Lists, hierarchies, and trees

OntologyThe ontology of a complicated

semantic system can capture enough knowledge so a computer can perform everyday knowledge◦To define a set of classes that together

cover a domain of interestFramework provides syntax,

vocabulary, and some pre-defined terms◦Framework is an ontology for constructing

ontology

Ontology ConsiderationsMerging Ontology

◦Terms and classes can by understood by more than one ontology

◦Can be accomplished by using same system (like OWL)

◦Even if able to merge, inconsistencies could jeopardize reliability

◦Imports of second ontology should be kept simple and be done so in small sections

Merging Ontology

Ontology ConsiderationsProblems with importing a large

Ontology ◦Vocabulary may change over time

once ontology is developed Already committed to the vocabulary that

is distributed ◦Can be limited by designer but no

solutions have been made available

Ontology LanguagesFrameworks with Web-like usesRDFS

◦ Resource Description Framework Schema Specification

◦ Base RDF language for describing ontology◦ Built on top of RDF

RDF makes statements about resources, making assertions about a subject

Every RDFS statement is a legal RDF Statement◦ RDF classes and properties

Together with standard classes, possible to give basic characteristics of classes for an ontology

Not enough power to express many constraints or logical properties

Ontology LanguagesOWL (Web Ontology Language)

◦Final Recommendation by W3C◦Built to standardize a more capable

Ontology Framework than RDFS Need to restrict Cardinality Express optionally Combine classes

Ontology SummaryTo be useful for the semantic Web, an

ontology language must be:◦ Able to reference concepts defined elsewhere on

Web◦ Sharable over the Web◦ Be able to work with one or more languages◦ Able to merge several different ontologies◦ Widely accepted as a standard◦ Expressive enough for serious use◦ Support logical functions that are needed to

conduct business of the semantic WebLast two points are questioned abilities of

OWL

LogicUses in the Semantic Web

◦ Applying and evaluating rules◦ Inferring facts that haven’t been explicitly stated◦ Explaining why a particular conclusion has been

reached◦ Detecting contradictory statements and claims◦ Specifying ontology and vocabulary of all kinds◦ Representing knowledge

Describing the kinds of things that may be said about a subject How those statements are to be understood

◦ The statement and execution of queries to obtain information from stores of data

◦ Combining information from distributed sources in a coherent way

LogicThere is considerable risk that an open

system will absorb contradictory or incorrect information

Most reasoning systems can not capture explanations◦Ones that are able to can not do so in a

uniform, easy to read wayMore current versions of RDF define ways

to understand a collection of RDF statements that can deal with the possibility of contradictory information◦Requires more computing power

LogicLogic and Ontology

◦Ontology defines concepts and terms◦Logic provides ways to make

statements that define the use of concepts and terms To reason about collections of statements

that use the concepts and terms

LogicLogic and Representing

Knowledge◦Logic is a formal discipline dealing

mostly with formal language that can express a subset of everything that can be articulated using natural language

◦Formal description of data and information naturally involves the use of logic

LogicQueries

◦Logical descriptions of information to be retrieved from a database

◦Queries will need to operate across distributed sources of data to be effective in the Semantic Web Needs to reconcile the differences in

ontology and deal with problems of contradictory data

LogicProblems of Semantic Web logic looks to

deal with◦When trying to decide what data should be

imported from remote database Size of the knowledge base might be too large and

overwhelm resources◦ Importing data without duplicating knowledge

How much is interconnected? Don’t want to import automatically because of a

formation of any new data◦ Importing unreliable information

Contaminate good data

TrustWith development in utility of Web,

trust needs to be established between system and user

Trust◦Identity: Who are you?◦Why should I trust you?◦Who else trusts you?◦How much should I trust you?◦How do I know that you said what you

claimed you have said?

TrustBelief

◦How much confidence should I place in what you say?

◦What should I believe when different facts don’t agree

◦How much should my prior beliefs influence my confidence in what you say?

◦How can I establish the correct degree of belief for a given set of information?

Tools of TrustKeys – Private and PublicDigests

◦Special summary of a document or message that can not be reversed to the original, no key needed

◦Slight differences in messages amount to large differences in digest

◦Similarity of digests can not be used to predict similarity in messages

Tools of TrustPublic Key Infrastructure (PKI)

◦ Widespread system◦ Certificate Authority (CA) issues digital certificate

CA trustworthy source CA signs certificate for other CAs

◦ Creates chain of certifications, eventually amounting to a size that alleviates issues of trust

◦ Potential problems If CA private key compromised, entire chain untrustworthy Large cross-certified chains can become unmanageable CAs may have different standards Human error and fraud

Digital Signatures◦ Authenticated by CA or CA chain

Video

The Semantic Web

Work CitedPassin, T. B. Explorer's guide to the semantic web. Manning

Publications, 2004. Print.

http://www.w3schools.com/web/web_semantic.asp

http://www.semanticfocus.com/media/insets/semantic-web-layer

cake-2.pnghttp://www.xml.com/2003/02/05/graphics/graph1.gif

http://www.codeproject.com/KB/books/GuideSemanticWeb/img002.jpg

http://searchsoa.techtarget.com/definition/Semantic-Web

http://semanticweb.org/wiki/Semantic_Web