Resource Description Framework - RDF 4 / 4 / 2016 Wameed Deyah Iraq - Babylon University - IT College - Info Net Department 1

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 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 from 10. February 2004 2 2

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 3 3

The purpose of RDF RDF was designed to provide a common way to describe information so it can be read and understood by computer applications. RDF descriptions are not designed to be displayed on the web. 4 4

RDF/XML RDF documents are written in XML. The XML language used by RDF is called RDF/XML. By using XML, RDF information can easily be exchanged between different types of computers using different types of operating systems and application languages. 5 5

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: 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" (note that a property value can be another resource) 6 6

Example The following RDF document could describe the resource "http://www.w3schools.com/rdf": <?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> 7 7

RDF Statements The combination of a Resource, a Property, and a Property value forms a Statement (known as the subject, predicate and object of a Statement). Let's look at some example statements to get a better understanding: Statement: "The author of http://www.w3schools.com/rdf is Jan Egil Refsnes". The subject of the statement above is: http://www.w3schools.com/rdf The predicate is: author The object is: Jan Egil Refsnes Statement: "The homepage of http://www.w3schools.com/rdf is http://www.w3schools.com". The predicate is: homepage The object is: http://www.w3schools.com 8 8

Introduction XML does not provide any means of talking about the Semantics (meaning) of data. Suppose we want to express the following fact: David Billington is a lecturer of Discrete Mathematics. There are various ways of representing this sentence in XML. Three possibilities are: <course name="Discrete Mathematics"> <lecturer>David Billington</lecturer> </course> 2. <lecturer name="David Billington"> <teaches>Discrete Mathematics</teaches> </lecturer> 3. <teachingOffering> <course>Discrete Mathematics</course> </teachingOffering> 9 9

Introduction (Cont.) RDF is essentially a data-model. Its basic building block is an object-attribute-value triple, called a statement. It is up to users to define their own terminology in a schema language called RDF Schema (RDFS). <academicStaffMember>Grigoris Antoniou</academicStaffMember> <professor>Michael Maher</professor> <course name="Discrete Mathematics"> <isTaughtBy>David Billington</isTaughtBy> </course> Is it correct from the XML viewpoint? Is it correct from the RDFS viewpoint? 10 10

Fundamentals of RDF Resources Properties Statement 11 11

Resources We can think of a resource as an object, a “thing” we want to talk about (authors, books, publishers, places, people, hotels, rooms and so on). Every resource has a URI, a Universal Resource Identifier. A URI can be a URL (Unified Resource Locator, or Web address) or some other kind of unique identifier not only for web-locations but also for such diverse objects as telephone numbers, ISBN numbers and geographic locations. 12 12

Properties Properties are a special kind of resources; they describe relations between resources (“written by”, “age”, “title”, and so on). 13 13

Statements A statement is an object-attribute-value triple, consisting of a resource, a property, and a value. Ex / David Billington is the owner of the Web page http://www.cit.gu.edu.au/∼db. (“David Billington”, http://www.mydomain.org/site-owner, http://www.cit.gu.edu.au/∼db). We can think of this triple (x, P, y) as a logical formula P(x, y), where the binary predicate P relates the object x to the object y. 14 14

Statements (Cont.) 15 15

Statements (Cont.) ( http://www.cit.gu.edu.au/∼db, http://www.mydomain.org/site-owner, “David Billington”) ( “David Billington”, http://www.mydomain.org/phone, “3875507”) ( “David Billington”, http://www.mydomain.org/uses, http://www.cit.gu.edu.au/∼arock/defeasible/De easible.cgi) (“www.cit.gu.edu.au/∼arock/defeasible/Defeasible.c gi”, http://www.mydomain.org/site-owner, “Andrew Rock”) 16 16

RDF Elements Graphs are a powerful tool for human understanding. But the Semantic Web vision requires machine-accessible and machineprocessable representations. Therefore, there is another representation possibility based on XML. rdf:RDF tags: The content of this element is a number of descriptions, which use rdf:Description tags to make a statement about the resource . • an about attribute, referencing an existing resource. • an ID attribute, creating a new resource. 17 17

RDF Elements 18 18 <?xml version="1.0" encoding="UTF-16"?> <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:mydomain="http://www.mydomain.org/my-rdf-ns"> <rdf:Description rdf:about="http://www.cit.gu.edu.au/~db"> <mydomain:site-owner>David Billington</mydomain:site-owner> </rdf:Description> </rdf:RDF> 18 18

Reification statements about statements For example Grigoris believes that David Billington is the creator of the Web page http://www.cit.gu.edu.au/∼db. 19 19

Data Types In RDF, typed literals are used to provide the type of data (“David Billington”, http://www.mydomain.org/age, “27”^^http://www.w3.org/2001/XMLSchema#integer ) The most widely used data typing scheme will be the one by XML Schema. XML Schema predefines a large range of data types, including Booleans, integers and floating-point numbers, times and dates. 20 20

A Critical View of RDF referee(X, Y, Z) is: X is the referee in a chess game between players Y and Z. We now introduce a new auxiliary resource chessGame and the binary predicates ref, player1, and player2. Then we can represent referee(X, Y, Z) as follows: ref(chessGame, X) player1(chessGame, Y) player2(chessGame, Z) 21 21

A Critical View of RDF (Cont.) 22 22

A Critical View of RDF (Cont.) Problems: The original predicate with three arguments was simpler and more natural. Properties are special kinds of resources. Therefore, properties themselves can be used as the object in an object-attribute-value triple (statement). While this possibility offers flexibility, it is rather unusual for modeling languages, and can be confusing for modelers. The reification mechanism introduces a level of complexity that is not necessary for a basic layer of the Semantic Web. the XML-based syntax of RDF is well suited for machine processing but is not particularly human-friendly. 23 23

<. DOCTYPE owl [<. ENTITY xsd "http://www. w3 <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns:xsd="http://www.w3.org/2001/XLMSchema#" xmlns:uni="http://www.mydomain.org/uni-ns#"> <rdf:Description rdf:about="949352"> <uni:name>Grigoris Antoniou</uni:name> <uni:title>Professor</uni:title> </rdf:Description> <rdf:Description rdf:about="949318"> <uni:name>David Billington</uni:name> <uni:title>Associate Professor</uni:title> <uni:age rdf:datatype="&xsd;integer">27</uni:age> <rdf:Description rdf:about="949111"> <uni:name>Michael Maher</uni:name> <rdf:Description rdf:about="CIT1111"> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy>David Billington</uni:isTaughtBy> <rdf:Description rdf:about="CIT1112"> <uni:courseName>Concrete Mathematics</uni:courseName> <uni:isTaughtBy>Grigoris Antoniou</uni:isTaughtBy> <rdf:Description rdf:about="CIT2112"> <uni:courseName>Programming III</uni:courseName> <uni:isTaughtBy>Michael Maher</uni:isTaughtBy> <rdf:Description rdf:about="CIT3112"> <uni:courseName>Theory of Computation</uni:courseName> <rdf:Description rdf:about="CIT3116"> <uni:courseName>Knowledge Representation</uni:courseName> </rdf:RDF>   24 24

The rdf:resource Attribute <rdf:Description rdf:about="CIT1111"> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy rdf:resource="949318"/> </rdf:Description> <rdf:Description rdf:about="949318"> <uni:name>David Billington</uni:name> <uni:title>Associate Professor</uni:title> 25 25

The rdf:resource Attribute (Cont.) <rdf:Description rdf:about="CIT1111"> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy rdf:resource=“#949318"/> </rdf:Description> <rdf:Description rdf:ID=“#949318"> <uni:name>David Billington</uni:name> <uni:title>Associate Professor</uni:title> 26 26

Nested Descriptions <rdf:Description rdf:about="CIT1111"> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy rdf:resource="949318"> <rdf:Description rdf:about="949318"> <uni:name>David Billington</uni:name> <uni:title>Associate Professor</uni:title> </rdf:Description> <uni:isTaughtBy> 27 27

The rdf:type Element 28 28 <rdf:Description rdf:about="CIT1111"> <rdf:type rdf:resource="&uni;course"/> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy rdf:resource="949318"/> </rdf:Description> <rdf:Description rdf:about="949318"> <rdf:type rdf:resource="&uni;lecturer"/> <uni:name>David Billington</uni:name> <uni:title>Associate Professor</uni:title> 28 28

Abbreviated Syntax It is possible to abbreviate the syntax of RDF documents. The simplification rules are: Childless property elements within description elements may be replaced by XML attributes, as in XML. For description elements with a typing element we can use the name specified in the rdf:type element instead of rdf:Description. 29 29

Abbreviated Syntax (Cont.) <rdf:Description rdf:ID="CIT1111"> <rdf:type rdf:resource="&uni;course"/> <uni:courseName>Discrete Mathematics</uni:courseName> <uni:isTaughtBy rdf:resource="#949318"/> </rdf:Description> (according to rule 1 applied to uni:courseName) equivalent to <rdf:Description rdf:ID="CIT1111" uni:courseName="Discrete Mathematics"> (according to rule 2) <uni:course rdf:ID="CIT1111“ uni:courseName="Discrete Mathematics"> </uni:course> 30 30

Thanks for your paitence (Cont.) To be continue … Thanks for your paitence 31 31

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