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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By Malak Bagais
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.
To understand sentences is to represent Web content in a form that is
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 Semantic Web
The layered-language model (Courtesy of W3C, 2001)
Unicode is a character set that provides a unique number to every character irrespective of the platform, program, and the language.
Generic URI syntax
<URI> := <scheme> : <scheme-specific-part>
Are special kinds of URIs that
<URN> := urn: <namespace> : <namespace-specific-part>
Example of a web page of a Student Service Center
Example of a web page of a Student Service Center
Captures data relationships and their associated meaning
Is a specification of a conceptualization
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).
Developing an ontology includes:
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
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
Document Type Definition (DTD)
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.
An XML document college.xml
<college name= College of Engineering>
An ordered labeled tree
A language for limiting the structure of XML documents.
Constructs in an XML Schema:
Example of an XML schema
Database of books
To maintain record of books by ISBN
A brief history of time
gives truly intimate glimpses into the intricacies of both the universe and Hawking himself.
XML document college.xml
Tree representation for college.xml
Query 1: Select all lecturer elements.
The expression selects all lecturer elements, which are children of the college element node that resides immediately below the root node.
Query 2: Select all lecturer elements.
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.
Query 3: Select all courses with the 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.
Query 4: Select all title attribute nodes within course elements anywhere in the document, which have the value “Nonlinear Analysis”.
//course[@title="Nonlinear Analysis"][email protected]
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.
Tree representation for Queries 3 and 4
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
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
<?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>
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 identifies things using Web identifiers (URIs), and describes resources with properties and property values.
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.
<?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>
The combination of a Resource, a Property, and a Property value forms a Statement (known as the subject, predicate and object of a Statement).
"The author of http://www.w3schools.com/rdf is Jan EgilRefsnes".
Object: Jan EgilRefsnes
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.
Using a graph to represent metadata
Fragment of an RDF