a semantic web primer 1. chapter

A Semantic Web Primer

1. Chapter The Semantic Web Vision

염붕 2006.01.10

Contents

1. Today’s Web 2. From Today’s Web to the Semantic

Web: Examples 3. Semantic Web Technologies 4. A Layered Approach

1 Today’s Web(1/4)

• The World Wide Web has also changed the way we think of computer.

Originally, computing numerical calculations currently, information processing, databases, games Now, entry points of information highway

• Typical uses of the web today . -seeking and making use of information -searching for and getting in touch with other people -reviewing catalogs of online stores and ordering products

1 Today’s Web(2/4)

• There are serious problems associated with Keyword-based search engines’ use:

-High recall, low precision.

◆ Mildly relevant or irrelevant document .

-Low or no recall. ◆ Less frequent problem, it dose occur.

-Results are highly sensitive to vocabulary.

◆ Use different terminology from the original query. Return similar results.

-Results are single Web pages .

◆ Manually extract information, time consuming activity.

1. Today’s Web(3/4)

• The obstacles to providing better support to Web users.

-Manually extract the information costs much time.

-The meaning of Web content is not machine accessible.

◆ When interpreting sentences and extracting useful information, the capabilities of current software are still very limited.

EX1: I am a professor of computer science. I am a professor of computer science, you may think…

1. Today’s Web(4/4)

• A alternative approach is to represent Web content.

-More easily machine processable. -Use intelligent techniques.

• The Semantic Web will not be a new global information highway parallel to the existing Web.

• The semantic web will evolve out of the existing web.

2. From Today’s Web to the Semantic web

-Knowledge Management -B2C Ecommerce -B2B Ecommerce -Personal Agents

Examples

2. From Today’s Web to the Semantic web(1/6)

• Knowledge Management concerns itself with acquiring, accessing, and maintaining knowledge.

• The current technology suffers from limitations as follows:

-Searching information. ◆ Depend on keyword based search engines. -Extracting information. ◆ Manually browse the retrieved documents for relevant information. -Maintaining information. ◆ Inconsistencies in terminology and failure to remove outdated information. -Uncovering information. ◆ New knowledge in corporate databases is extracted using data mining. -Viewing information. ◆ Restrict access to certain information to certain groups of employees. Hard

to realize over the web.

2.1 Knowledge Management


• The Semantic web is to allow much more advanced knowledge management system.

-Knowledge will be organized in conceptual spaces according to its meaning.

-Automated tools will support maintenance by checking for inconsistencies and extracting new knowledge.

-Keyword based search will be replaced by query answering: requested knowledge will be retrieved, extracted ,and presented in a human friendly way.

-Query answering on several documents will be support. -Defining who may view certain parts of information will be

possible.


• A typical scenario of B2C Ecommerce -Visiting one or several online shops -Browsing their offers -Selecting and ordering products

• The disadvantage of today’s Web.

-manual browsing is too time-consuming

-A user will only visit one or a very few online stores before making a decision.

2.2 B2C E-Commerce


• To alleviate this situation one wrapper per store must be developed.

-tools for shopping around on the web . -visit shops, extract information, compile a market overview. -these functionalities are provided by wrapper.

• The drawbacks of the approach. -Only limited information is extracted. -Programming wrappers is time consuming -Changes in the online store outfit require costly

reprogramming.


• The Semantic Web will allow the development of software agents that can interpret the product information and terms of service.

-Pricing and product information will be extracted online shops, and delivery and privacy policies will be interpret and compared to the user requirements.

-Additional information about the reputation of online shops. Will be retrieved from other sources.

-The low level programming of wrappers will become obsolete.

-more sophisticated shopping agents will be able to conduct automated negotiations, on the buyer’s behalf.


• The Internet appears to be an ideal infrastructure for business to business communication.

-B2B e-commerce is hampered by the lack of standards. -HTML provides neither the structure nor the semantic of

information.• The new standard of XML is a big improvement .• The realization of the Semantic Web will allow

business to enter partnerships without much overhead. Differences in terminology will be resolved using standard abstract domain models, and data will be inter changed using translation services.

2.3 B2B E-Commerce

3. Semantic Web Technologies

-explicit Metadata-Ontologies-Logic-Agents

Technologies’ contents


Keyword-based search agents.• EX2: Physiotherapy Center.<h1>Agilitas Physiotherapy Center</h1> Welcome to the homepage of the Agilitas

physiotherapy center. Do you feel pain? Have you had an injury? Let our staff Lisa Davenport, Kelly Townsend (our lovely secretary) and Steve Matthews take care of your body and soul…

3.1 Explicit Metadata


The Semantic Web intelligent agents.<company> <treatmentoffered>physiotherapy</treatmentoffered> <companyName>Agilitas physiotherapy

center</companyName> <staff> <therapist>Lisa Davenport</therapist> <therapist>Steve Matthews</therapist> <secretary>Kelly Towmsend</secretary> </staff></company>


• Explicit Metadata : data about data ,capture part of the meaning of data .

• The greatest current challenge is not scientific but rather one of technology adoption.

• HTML should be replaced by more appropriate languages.


• The term ontology comes from philosophy.• An ontology consists of a finite list of terms

and the relationships between these terms.• Ontologies are useful for the organization and

navigation of Web sites • For improving the accuracy of Web searches.

3.2 Ontologies


University people

Staff Students

Under graduate PostgraduateAdministration staff Technical support staffAcademic staff

Regular faculty staff

Research staff

Visiting staff

EX3: A university setting.

Figure 1. University Setting


• At present the most important ontology languages for Web are :

-XML, provide a surface syntax for structure documents.

-XML, Schema a language for restricting the structure of xml document.

-RDF, a data model for objects and relations between them

-RDF Schema, a vocabulary description language -OWL, a richer vocabulary description language


• Logic offers formal languages for expressing knowledge .

• Logic provide us with well understood formal semantic

• Making implicit knowledge explicit. EX4: professor (X) faculty (Y) faculty (Y) staff (X) professor (Michael)

Then we can deduce the following : faculty (Michael ) staff (Michael) professor (X) staff (X)

3.3 Logic


• The important advantage of logic is that it can provide explanations for conclusions.

-Explanations are important for the Semantic Web because they increase user’s confidence in semantic web agents.

-Explanations will also be necessary for activities between agents.

◆some agents will be able to draw logical conclusions, others will only have the capability to validate proofs, to check whether a claim made by another agent is substantiated.


• Agents are pieces of software that work autonomously and proactively .

• Semantic web agents will make use of all technologies we have outlined:

-metadata, identify and extract information form Web sources.

-ontologies, assist in Web searches. Interpret information, communicate with other agents.

-logic, processing retrieved information, drawing conclusions.

3.4 Agents


users

Present in web browser

Search engine

WWW

Users

Personal agent

Intelligent infrastructure services

WWW figure 2 Intelligent personal agents

4. A Layered Approach(1/3)

• The development of the semantic web proceeds in steps.

• In each step, a layer is built on top of another .• In building one layer of the semantic web on top

of another, two principles should be followed: -downward compatibility. ◆A layer should be able to interpret and use information written at lower

levels.

-upward partial understanding. ◆A layer should take at least partial advantage of information at higher l

evels.


Unicode URI

XML +NS +xml schema

RDF + rdf schema

Ontology vocabulary

Logic

Proof

Trust Dig

ital sig

natu

re

figure 3 A “layered cake” of the semantic web

◆A layered approach to the Semantic Web


• At the bottom is XML, a particularly suitable for sending documents across the Web.

• RDF is a basic data mode, It is located on top of the XML layer.

• RDF Schema a primitive language for writing ontologies, is based on RDF.

• Logic is used to enhance the ontology language further.

• Trust is located at the top of the pyramid.

a semantic web primer 1. chapter

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semantic web primer

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meaning of web content