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Semantic Web. Quratulain Rajput Faculty of Computer Science, IBA Spring2013. Semantic Web Technologies. How thing can be identified How knowledge can be expressed

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Semantic web

Semantic Web

Quratulain Rajput

Faculty of Computer Science, IBA

Spring2013


Semantic web technologies
Semantic Web Technologies

  • How thing can be identified

  • How knowledge can be expressed

  • How models that lay behind or above this represented facts can also be explicitly represented with in the web using languages of semantic web.

Quratulain Rajput


Semantic web technologies1
Semantic Web Technologies

Quratulain Rajput


A layered approach
A Layered Approach

Quratulain


A layered approach1
A Layered Approach

  • The development of Semantic Web proceeds in steps, each step building a layer on top of another.

  • The purpose of layered approach is that it is easier to achieve consensus on small steps.

Quratulain


A layered approach2
A Layered Approach

  • In building a Semantic Web layer two principal should be followed:

    • Downward compatibility

    • Upward partial understanding

Quratulain


Semantic web layers
Semantic Web Layers

  • URL:

    • E.g www.iba.edu.pk

  • URI:

    • E.ghttp://dbpedia.org/resource/pakistan

  • XML layer

    • Syntactic basis

  • RDF layer

    • RDF basic data model for facts

    • RDF Schema simple ontology language

  • Ontology layer

    • More expressive languages than RDF Schema

    • Current Web standard: OWL


Semantic web layers1
Semantic Web Layers

  • Logic layer(writing of rules)

    • enhance ontology languages further

    • application-specific declarative knowledge

  • Proof layer (execution of rules)

    • Proof generation, exchange, validation

  • Trust layer (evaluates whether to trust the proof or not)

    • Digital signatures

    • recommendations, rating agencies ….


RDF

  • RDF(Resource Description Framework), document describes as directed graph.

  • In contrast, XML is encoded in tree structure.

  • Tree structure processed efficiently then why need graphs. Reasons are:

    • RDF is not for structuring the documents, but rather for describing general relationships between object of interest (semantic knowledge). which is natural represent in the form of graphs.

    • RDF is description language for data on web , where web store manage data in decentralized way. Easy to combine graph structure form multiple sources.

Quratulain Rajput


URI

  • To distinguish resources from each other.

  • Every URL is a valid URI

  • URI also used as identifiers in RDF document that has clear identity in the context of the given application: books, places, people, event etc.

  • URI that are not URL are some time called URN(Uniform Resource Names), exclusively for unique identification (directory path)

Quratulain Rajput


From graph to triple
From Graph to Triple

  • In graph, situation become complicated for storage and management as the size of graph increases.

  • Therefore, represent graph as character strings.

  • RDF represent using following syntax:

    • Turtle

    • XML (most commonly used syntax b/c many programming languages support it)

Quratulain Rajput


RDF

  • XML is a TREE structure while RDF is Graph.

  • XML does not provide any semantics about data.

    • For example: no meaning associated with the nesting of tags.

  • RDF data model is an abstract, conceptual layer independent of XML

    • consequently, XML is a transfer syntax for RDF, not a component of RDF

    • RDF data might never occur in XML form

Quratulain


Introduction
Introduction

No standard way of assigning meaning to tags nesting

  • Suppose to express the fact:

    Ahmed is a lecturer of Discrete Mathematics

  • Possibilities are:

    <course name=“Discrete Mathematics”>

    <lecturer> Ahmed </lecturer>

    </course>

    <lecturer name=“Ahmed”>

    <teaches>Discrete Mathematics</teaches>

    </lecturer>

    <teachingOffering>

    <lecturer>Ahmed</lecturer>

    <course>Discrete Mathematics </course>

    </teachingOffering>

Quratulain


RDF

  • RDF is a data model.

  • Its basic building block is an object-attribute-value triple, called statement.

  • Syntax in XML (standard by W3C)

  • Domain independent, It is up to user to define their own terminology in schema called RDFS

Quratulain


RDF

value

resource

property

  • Fundamental concept of RDF are

    • Resource

    • Properties

    • Statements

Quratulain


Resource
Resource

  • Resource is an object (we want to talk about)

    • Ex. Book, places, people, hotel and so on.

  • Every resource has URI.

    • URI can be a URL or some kind of unique identifier

Quratulain


Properties
Properties

  • Describe relationship between resource.

    • Ex. writtenBy, age, title, etc

  • Properties in RDF are also identified by URI

Quratulain


Statement
Statement

  • A statement is an object-attribute-value triple, consisting of a resource, property and a value.

  • Value can be either resource or literal.

Quratulain


Example
Example

  • The owner of web page (http://www.iba.edu.pk/faculty) is Wasim

http://www.iba.edu.pk/faculty

owner

Wasim

<rdf:Descriptionrdf:about=“http://ww.iba.edu.pk/faculty”>

<owner> Wasim </owner>

</rdf:Description>

Quratulain


Logical formula
Logical formula

http://www.iba.edu.pk/faculty

owner

Wasim

As logical formula P(x,y), where P is binary predicate relates object Wasim to object http://www.iba.edu.pk/faculty.

Quratulain


Example1
Example

  • Sana knows Asif.

  • Sana’s surname is Malik.

  • Asif knows Faisal.

  • Salman works with Faisal.

    How would you represent this? Draw graph.

Quratulain


Example2
Example

Subject

Object

Predicate

knows

knows

Sana

Asif

Faisal

worksWith

surName

Literal

Salman

“Malik”

Quratulain


Reading assignment
Reading Assignment

  • http://www.huffingtonpost.com/steve-hamby/semantic-web-technology_b_1228883.html

Quratulain Rajput


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