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Chapter 9 The Semantic Web. By Malak Bagais. The Semantic Web . Initiated by Tim Berners-Lee, the inventor of the World Wide Web. A common framework that allows data to be shared and reused across application, enterprise, and community boundaries.

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the semantic web
The Semantic Web

Initiated by Tim Berners-Lee, the inventor of the World Wide Web.

A common framework that allows data to be shared and reused across application, enterprise, and community boundaries.

Link smaller elements of data and information and further assign meaning to the links between data elements.

semantic web initiative
Semantic Web Initiative

To understand sentences is to represent Web content in a form that is

  • more easily machine-processible and
  • use intelligent techniques to take advantage of these representations.
trend in semantic web
Trend in Semantic Web

Providing a common syntax for machine understandable statements

Establishing common vocabularies

Agreeing on a logical language

Using the language for exchanging proofs

a layered structure for the semantic web
A layered Structure for the Semantic WEB

A layered structure for Semantic Web

  • Unicode/URI
  • XML/Name Spaces/ XML Schema
  • RDF/RDF Schema
  • Ontology vocabulary
  • Logic
  • Proof
  • Trust
unicode
Unicode

Unicode is a character set that provides a unique number to every character irrespective of the platform, program, and the language.

uniform resource identifiers uris
Uniform Resource Identifiers (URIs)

Generic URI syntax

<URI> := <scheme> : <scheme-specific-part>

Example:

uniform resource names urns
Uniform Resource Names (URNs)

Are special kinds of URIs that

  • map other namespacesinto URN-space,
  • are required to remain globally unique and persistent,
  • can be specified in a single line of text,
  • have the scheme urn.

<URN> := urn: <namespace> : <namespace-specific-part>

Examples

  • urn:isbn:0-395-36341-1
  • urn:newsml:reuters.com:20000206:IIMFFH05643_2004-08-03_17-54-01_L06154
uniform resource locator url
Uniform Resource Locator (URL)
  • Another special type of URI
  • used to identify an Internet resource
  • Difference between URL, URN, and URI:
    • URL:http://www.tmrf.org/kpr/issue1.htm
    • URN: www.tmrf.org/kpr/issue1.htm#one
    • URI:http://www.tmrf.org/kpr/issue1.htm#one
markup
Markup

Example of a web page of a Student Service Center

explicit metadata
Explicit Metadata

Example of a web page of a Student Service Center

ontology
Ontology

Captures data relationships and their associated meaning

Is a specification of a conceptualization

ontology1
Ontology

An ontology is a precise narrative of concepts in a field of discourse (classes or concepts), properties of each concept narrating various features and attributes of the concept (slots or roles or properties), and restrictions on slots (facets or role restrictions).

ontology development
Ontology development

Developing an ontology includes:

  • defining classes in the ontology
  • arranging the classes in a taxonomic (subclass–superclass) hierarchy
  • defining attributes/relationshipsand describing allowed values for these slots
  • filling in the values of slots for instances
reasons for creating ontologies
Reasons for creating ontologies

to distribute common understanding of the information structure between individuals or software agents

to facilitate reuse of domain knowledge

to formulate exact domain assumptions

to split domain knowledge from operational knowledge

to analyze domain knowledge

ontology language
Ontology language

XML

presents syntax for structured documents but enforces no semantic constraints on the meaning of these documents.

is a Hierarchical data model

is a syntax specification for data markup

encloses data in tags

tags can relate to the meaning of the enclosed text

tags are extensible

related technologies
Related Technologies

Document Type Definition (DTD)

XML Schema

DOM

XPath

XLinks

XPointers

XSLT

advantages of xml
Advantages of XML

An XML document holds tags that indicate data types of every element.

It is straightforward to insert related data to a node in an XML document without formatting the document cumbersome.

There is nothing about XML that binds it to a specific operating system or technology.

There are numerous object-based parsers available for XML.

xml example of a college
XML Example of a College

An XML document college.xml

<location name=Innsbruck>

<college name= College of Engineering>

<deptcode>CIS</deptcode>

</college>

</location>

data model
Data Model

An ordered labeled tree

xml schema
XML Schema

A language for limiting the structure of XML documents.

Constructs in an XML Schema:

  • simple type definitions
  • complex type definitions,
  • attribute
  • element declaration
illustration of xml communication
Illustration of XML Communication

Database of books

To maintain record of books by ISBN

<document id="1">

Hawking’s

<book isbn="0553103741">

A brief history of time

</book>

gives truly intimate glimpses into the intricacies of both the universe and Hawking himself.

</document>

xml query languages
XML Query Languages
  • path expression
  • Xpath, Xquery, XQL, and XML-QL
  • XPath
    • syntax for defining parts of an XML document
    • It uses path expressions to navigate in XML documents.
    • It includes almost 100 built-in functions and has become a W3C standard from 1999.
xml document
XML Document

XML document college.xml

tree representation of an xml document
Tree Representation of an XML Document

Tree representation for college.xml

xpath query language
XPath Query Language

Query 1: Select all lecturer elements.

/college/lecturer

The expression selects all lecturer elements, which are children of the college element node that resides immediately below the root node.

xpath query language1
XPath Query Language

Query 2: Select all lecturer elements.

//lecturer

In this expression, // says that you must consider every element in the document and check whether they are of type lecturer. This path expression selects all lecturer elements present anywhere in the document.

The tree representation of this query is identical to the tree representation of Query 1.

xpath query language2
XPath Query Language

Query 3: Select all courses with the title “Nonlinear Analysis”.

//course[@title="Nonlinear Analysis"]

Here, the test within square brackets restricts the set of selected nodes. The expression selects course elements with the title that satisfies a particular condition.

xpath query language3
XPath Query Language

Query 4: Select all title attribute nodes within course elements anywhere in the document, which have the value “Nonlinear Analysis”.

//course[@title="Nonlinear Analysis"]/@title

This expression collects title attribute nodes of the course elements. The symbol @ denotes the attribute nodes.

The tree representation of queries 3 and 4 is given in next figure.

what is rdf
What is RDF?

RDF stands for Resource Description Framework

RDF is a framework for describing resources on the web

RDF is designed to be read and understood by computers

what is rdf1
What is RDF?

RDF is not designed for being displayed to people

RDF is written in XML

RDF is a part of the W3C\'s Semantic Web Activity

RDF is a W3C Recommendation

rdf document
RDF document

<?xml version="1.0"?><rdf:RDFxmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"xmlns:si="http://www.w3schools.com/rdf/"><rdf:Descriptionrdf:about="http://www.w3schools.com">  <si:title>W3Schools</si:title>  <si:author>Jan EgilRefsnes</si:author></rdf:Description></rdf:RDF>

rdf examples of use
RDF- Examples of use

Describing properties for shopping items, such as price and availability

Describing time schedules for web events

Describing information about web pages (content, author, created and modified date)

Describing content and rating for web pictures

Describing content for search engines

Describing electronic libraries

rdf resource property and property value
RDF Resource, Property, and Property value

RDF identifies things using Web identifiers (URIs), and describes resources with properties and property values.

explanation of resource property and property value
Explanation of Resource, Property, and Property value

A Resource is anything that can have a URI, such as "http://www.w3schools.com/rdf"

A Property is a Resource that has a name, such as "author" or "homepage"

A Property value is the value of a Property, such as "Jan Egil Refsnes" or http://www.w3schools.com.

example
Example

<?xml version="1.0"?><RDF>  <Description about="http://www.w3schools.com/rdf">    <author>Jan Egil Refsnes</author>    <homepage>http://www.w3schools.com</homepage>  </Description></RDF>

rdf statement
RDF Statement

The combination of a Resource, a Property, and a Property value forms a Statement (known as the subject, predicate and object of a Statement).

example1
Example

Statement:

"The author of http://www.w3schools.com/rdf is Jan EgilRefsnes".

Subject: http://www.w3schools.com/rdf

Predicate: author

Object: Jan EgilRefsnes

rdf graph
RDF Graph

The underlying structure of any expression in RDF is a collection of triples, each consisting of a subject, a predicate and an object. A set of such triples is called an RDF graph

The direction of the arc is significant: it always points toward the object.

rdf graph example
RDF Graph Example

http://www.w3schools.com/rdf

Jan EgilRefsnes

author

use of rdf to describe this book
Use of RDF to Describe This Book

Using a graph to represent metadata

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