Semantic Web - an introduction By Daniel Wu (danielwujr)

Semantic Web - an introduction

By Daniel Wu (danielwujr)

Presentation Outline

(Why) Problem Definition

(Who and When) Semantic Web (SW) Proposal

(What) SW Features & Services

(How) SW KR* & Layers

(Where) SW Current Status

*knowledge representation








Semantic?

• Assalamu alaikum

• Let’s give it semantic…– Assalamu alaikum is Arabian– Assalamu alaikum means “Hello”

• sēmantikós (Greek) = having meaning

Problem Definition

• Computer have no reliable way to process semantics on Web content.

• (Most of the Web’s content today is designed for humans to read.)

Semantic Web (SW) Proposal

• Tim Berners-Lee– inventor of the WWW

• 1998

Solution

1. Achieving a set of connected applications for data on the Web in such a way as to form a consistent logical web of data.

2. Develops languages for expressing information in a machine-processable form.

- Semantic Web Road map, Tim Berners-Lee








SW Features & Services

• Semantic Web• The semantic web is an evolving extension of the World Wide Web

in which web content can be expressed not only in natural language, but also in a form that can be understood, interpreted and used by software agents, thus permitting them to find, share and integrate information more easily.

• Source: W3C Semantic Web FAQ

http://en.wikipedia.org/wiki/World_Wide_Web

http://en.wikipedia.org/wiki/Web_content

http://en.wikipedia.org/wiki/Natural_language

http://en.wikipedia.org/wiki/Software_agent

http://en.wikipedia.org/wiki/Digital_integration

SW Features & Services (cont.)

• Benefits– data integration,

• whereby data in various locations and various formats can be integrated in one, seamless application;

– resource discovery and classification (vertical search)• provide better, domain specific search engine capabilities;

– cataloging• describing the content and content relationships available at

a particular Web site, page, or digital library;

– intelligent software agents• facilitate knowledge sharing and exchange;

SW Features & Services (cont.)

• However…– You probably won’t “see” SW– And this is Weak AI








SW Knowledge Representation & Layers

Semantic Web Layer Cake

• Uniform Resource Identifiers (URI)

– URI is a name. (a pointer) – Uniform Resource Locator (URL) is one form of URI– URI does not need to be accessible over the Internet

• EXtensible Markup Language (XML)

– XML provides a surface syntax for structured documents

– XML imposes no semantic constraints on the meaning of documents

• Resource Description Framework (RDF)

– RDF is a simple data model for referring to objects ("resources") and how they are related.

– RDF enable anyone to say anything about anything– Triples: subject, predicate, object– RDF is composed of URIs– Ex. Daniel study CS

• RDF schema

– RDF Schema is a vocabulary for describing properties and classes of RDF resources, with a semantics for generalization-hierarchies of such properties and classes.

– Ex. Dog SubClassOf Animal

• Web Ontology Language (OWL)

– OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointness), cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes.

Ontology

• Definition

• Example

• Ontology & Knowledge presentation

• Ontology & Building ontology

• Ontology & Folksonomy

• Ontology & Interoperability

Ontology - Definition

• (short version)– Ontologies are systems of formally defined related co

ncepts.

• (long version)– Ontologies define the concepts and relationships use

d to describe and represent an area of knowledge. Ontologies are used to classify the terms used in a particular application, characterize possible relationships, and define possible constraints on using those relationships.

Ontology - Example

• A company is a type organization.• An organization may have a product or a service.• An organization is a group of people. • An employer may be a person or an organization.• A person may be employed by an employer.• A person may be in a marriage with only one other perso

n at a time.• A marriage is a kind of romantic relationship.• A friendship is a kind of social relationship.• A romantic relationship is a kind of friendship.• A person may be socially related to another person.• A person must have a gender.

Ontology & Knowledge presentation

– Back to “Assalamu alaikum”– We need previous knowledge to fully unders

tand the concept of “Assalamu alaikum”– previous knowledge

= world view

= ontology

– Oh! “Assalamu alaikum” means “Hello”

Ontology & Building ontology

• Cyc– Top down approach– Defines ontology on its own– Centralized

• Semantic Web– Bottom up approach– Defines language to define ontology– Destributed

• Everyone defines his/her own ontologies!

Ontology & Folksonomy

• Can ontology not be hierarchical?

• Can ontology be built from folksonomy?

Interoperability between different ontologies

• The OWL language can express mappings between concepts in different ontologies. But if there are many ontologies, and many of them partially overlap, it is a non-trivial task to actually make the mappings between their concepts.



• However… It’s hard.

• Having same name doesn’t guarantee having same meaning

• A bad example…–嘟嚕嘟嚕嘟嚕嘟嚕達達達

• Wrong conversion…• Same name doesn’t guarantee same meaning

• Web Ontology Language (OWL)

– OWL adds more vocabulary for describing properties and classes: among others, relations between classes (e.g. disjointness), cardinality (e.g. "exactly one"), equality, richer typing of properties, characteristics of properties (e.g. symmetry), and enumerated classes.

• Logic and Proof

– Tools to query language for semantic web data sources

– DL (Description Logic), not FOL

• Trust and Digital signature

– Documents be parsed not just into trees of assertions, but into trees of assertions about who has signed what assertions.

SW Layers - Review

Semantic Web Layer Cake








SW Current Status

• Bump!– Tools problem– Ontology problem– Poor rule engine

performance

SW Current Status

• Important players - Google– Not taking actions– Ask question!

• Incompetence• Competition• Deception








Q & A

• Welcome!