semantic web rdf website

8/13/2019 Semantic Web Rdf Website

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Interoperabilityof Embedded Systems

Introduction to Semantic Webtechnologies

Postgraduate Degree inInformation Engineering


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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 a part of the W3C's Semantic Web Activity

RDF is a W3C Recommendation since 2004


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RDF - Examples of Use

RDF provides a common framework for expressinginformation so it can be exchanged between applicationswithout loss of meaning. Examples of use:

Describing properties for shopping items, such as price andavailability

Describing time schedules for web events

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

Describing content and rating for web pictures

Describing content for search engines

Describing electronic libraries

...


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RDF is Written in XML?

RDF is a data model

Resources are identified using URIs

Information is a set of statements (subject - predicate -object) Subject and predicate are always resources (i.e. identified by

URIs)

Objects may be URIs or literal

Every RDF document corresponds to an oriented andlabeled graph


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RDF can be Written in XML

Many serialization formats exist for the RDF data model:

Notation 3 (N3)

Turtle

RDF/XML an XML-based syntax

By using XML, RDF information can easily be exchanged betweendifferent types of computers using different types of operatingsystems and application languages

During this course we will use the RDF/XML serialization format


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RDF and "The Semantic Web"

The RDF language is a part of the W3C's SemanticWeb Activity

W3C's "Semantic Web Vision" is a future where:

Web information has exact meaning

Web information can be understood and processed bycomputers

Computers can integrate information from the web


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RDF is a W3C Recommendation

RDF became a W3C Recommendation on February 2004

RDF documents consists of set of triples defining a knowledge base

Each triple have a subject a predicate and an object

In RDF data sets each triple may belong to a named graph or to thedefault un-named graph.


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RDF Resource, Property, and PropertyValue

RDF identifies things using Web identifiers ( URIs), and describes resources withproperties and property values

This enables to represent RDF statements about resources as a graph of nodes andarcs representing the resources, and their properties and values

A Resource is anything identified by a URI

such as "http://www.w3.org/RDF/"

A Property is a Resource that in triples is used to connect the subject with the object

such as "http://example.org#author" or "http://www.example.com/homepage"

A Property value is the value of a Property

A literal such as Mario Rossi

Or a resurce lice http:// www.arces.unibo.it "
http://www.arces.unibo.it/http://www.arces.unibo.it/


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RDF URIs Unlike conventional hypertext, RDF URIs can refer to any identifiable

thing

including things that may not be directly retrievable on the Web

RDF in addition to describing such things as Web pages can alsodescribe cars, businesses, people, news events, etc.

In addition, RDF properties themselves have URIs, to preciselyidentify the relationships that exist between the linked items

In RDF is also possible to define resources with unknown URI, thisresources are called blank nodes


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The following RDF document could describe the resource http://arces.it

The example is simplified, rdf namespace is omitted

RDF document and default namespace

A set of statements begin

Specify subject

Subject

Predicates

Literal object

Resource object

RDF Resource, Property, and Property Value

Mario Rossi

http://www.unibo.it/home

http://arces.it

http://www.unibo.it/home

Mario Rossi
http://arces.it/http://arces.it/


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RDF Graphs

The underlying structure of anyexpression in RDF is a collection oftriples

each consisting of a subject, a

predicate and an object A set of such triples form an RDF

graph

This can be illustrated by a node

and directed -arc diagram in which each triple is

represented as a node-arc-nodelink


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RDF Graphs The direction of the arc is

significant: it always pointstoward the object

The nodes of an RDF graph areits subjects and objects

The assertion of an RDF triplesays that some relationship ,indicated by the predicate,holds between the thingsdenoted by subject and object

The meaning of an RDFgraph is the conjunction(logical AND) of thestatements corresponding to

all the triples it contains


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RDF Global Graph

As Linked Data URIs are globally unique and can be dereferenced into sets of RDFtriples

It is possible to imagine all LinkedData as one giant global graph

Linked Data applications operate ontop of this giant global graph

and retrieve parts of it bydereferencing URIs as required

Merging is a very powerful feature of RDF

Metadata may be defined by several(independent) parties and combinedby an application


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Blank nodes

John Doe

Mario Rossi

http://ns#person_AC

http://ns#person_AJohn Doe

Mario Rossi

http://ns#know

http://ns#fullName>

http://ns#homePage

http://ns#fullName


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ReificationSyntactic sugar used:

rdf:Statementrdf:subjectrdf:predicaterdf:object

Given the triple < URI_sub, URI_pred, URI_obj> the reification is operated by creating a statementinstance and relating it to the subject, the predicate and the object of the statement to be reified. This

allows to have a more abstract view of the knowledge base e.g. giving the possibility to assert that acertain statement is trustable or not.

URI_sub URI_objURI_pred

Ntriple syntax for reification _:statement_bn rdf:type rdf:Statement . _: statement_bn rdf:subject < URI_sub > . _: statement_bn rdf:predicate < URI_pred > . _: statement_bn rdf:object < URI_obj > .

rdf:subject

rdf:predicate

rdf:object

Rdf:Statementrdf:type


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RDF Example

Suppose we have two records from a CD-list:


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RDF Example The first line of the RDF document is the

XML declaration

The XML declaration is followed by theroot element of RDF documents:

The xmlns :rdf namespace , specifiesthat elements with the rdf prefix arefrom the namespace"http://www.w3.org/1999/02/22-rdf-syntax-ns#".

The xmlns :cd namespace , specifiesthat elements with the cd prefix arefrom the namespace"http://www.recshop.fake/cd#".

The element containsthe description of the resource identifiedby the rdf :about attribute

The elements: ,, , etc. areproperties of the resource.


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RDF Example

The graphical view of the RDF document:


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The Element

is the root element of an RDF document

It defines the XML document to be an RDF document

It also contains a reference to the RDF namespace:


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The Element

The < rdf :Description > element may identify the subjectresource with the about attribute

It contains statements that describe the subject


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The Element

The elements, artist, country, company, price, and year, are defined in thehttp://www.recshop.fake/cd# namespace

This namespace is outside RDF (and not a part of RDF)

The elements, artist, country, company, price, and year, must be defined by someoneelse (company, organization, person, etc. )


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Properties as Attributes

The property elements can also be defined aspredicates


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Properties as Resources

The statements objects can also be existingresources

In the example, the property cd:artist identifies the

object through the rdf:resource attribute


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The RDF Container Element

RDF Container classes:

rdf :Bag

rdf :Seq

rdf :Alt

Note - We will talk about RDFS (RDF Schema) Vocabulary

Description Language later Now let's focus on container elements


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The Element

The < rdf :Bag> element is asubclass of rdfs:Container

It is used to describe a list ofvalues that do not have to be ina specific order

It may contain duplicate values


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The Element

The < rdf :Seq > element is asubclass of rdfs:Container

It is used to describe anordered list of values

(for example inalphabetical order)

It may contain duplicate

values


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The Element

It is used to describe a list ofalternative values

the user is supposed to selectonly one of the values

The first member of thecontainer the value of therdf:_1 property, is the default choice.


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RDF Terms

In the previous examples we have talked about "listof values" when describing the container elements

In RDF these "values" are called members

So, we have the following:

A container is a resource that contains things

The contained things are called members


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The rdf:parseType="Collection" Attribute

RDF List


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RDF ListOrdered opened and closed (using rdf:nil ) lists are represented in RDF through

rdf:List rdf:first rdf:rest rdf:nil

The example below represents the ordered and closed list 3, 2, 1.

23 1

_b1 _b2 _b3 rdf:nil

rdf:first

rdf:rest rdf:rest

rdf:List

rdf:type

rdf:rest


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RDF Schema (RDFS)

RDF Schema (RDFS) is an extension to RDF

W3C references:

Primer: http://www.w3.org/TR/2004/REC-rdf-primer-20040210/

Concepts: http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/

Syntax: http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/

Semantics: http://www.w3.org/TR/2004/REC-rdf-mt-20040210/

Vocabulary: http://www.w3.org/TR/2004/REC-rdf-schema-20040210/

Test Cases: http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/
http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-testcases-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-schema-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-mt-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-syntax-grammar-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-concepts-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/http://www.w3.org/TR/2004/REC-rdf-primer-20040210/


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RDF Schema

RDF describes resources with properties, and values

RDF is domain -independent

RDF user communities need the ability to define

application-specific classes and properties RDF Schema provides a mechanism for describing specific

domains


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RDF Schema

RDF Schema

variously abbreviated as RDFS, RDF(S), RDF-S, or RDF/S

is a set of classes and properties

provides basic elements for the description ofontologies, otherwise called RDF vocabularies , intendedto structure RDF resources

RDF Schema provides a type system for RDF


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RDF Schema

The resources in the RDF Schema vocabulary have URI referenceswith the namespace

http://www.w3.org/2000/01/rdf-schema#

conventionally associated with the prefix rdfs:

Vocabulary descriptions (schemas) written in the RDF Schemalanguage are legal RDF graphs

RDF software that is not written to also process the additional RDFSchema vocabulary can still interpret a schema as a legal RDF graph consisting of various resources and properties

But it will not "understand" the additional built-in meanings of theRDF Schema terms


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RDFS schema vocabulary: classes

rdfs Resource: the class of everything

rdfs Class: the class of all classes

rdfs Literal: the class of literal values

rdfs Datatype: the class of data types

rdfs Container: the class of rdf containers i.e. rdf:Bag, rdf:Seq, rdf:Alt

rdfs ContainerMembershipProperty: the class of rdf selectors i.e. the properties rdf:_1, rdf:_2, ...

Classes describe abstract concepts or categories or set to which individualmay belong. An individual is bound to the classes it belongs to through the rdf:type property

RDFS schema vocabulary: properties


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rdfs domain defines the domain of a property

rdfs range: defines the range of a property

rdfs subClassOf: associates a class with its super-class

rdfs subPropetyOf: associates a property with its super-property

rdfs member: superproperty of rdf:_1, rdf:_2, etc.rdfs label: associates a resource to a human readable label

rdfs comment: ssociatres a resource to a human readable description

rdfs seeAlso: associates a resource to another one which provides additional detai

rdfs isDefinedBy: associates a resource to another one which provides the definition.

RDFS schema vocabulary: properties

Properties are relationships defined in the domain terminology and used tospecify domain assertions in the form of triples. Properties are represented aslabeled arcs when drawing of an RDF documents and the are always orientedtowards the statement object


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Classes

The rdfs :subClassOf property may be used to statethat one class is a subclass of another

Example

In order to define a student class as a subclass of theclass person, you have to specify the statement:

Classes


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The class rdfs :Literal is the class of literal values such as strings andintegers

rdfs:Literal is an instance of rdfs:Class

rdfs:Literal is a subclass of rdfs:Resource

rdfs :Datatype is the class of datatypes

All instances of rdfs:Datatype correspond to the RDF model of adatatype

rdfs:Datatype is both an instance of and a subclass of rdfs:Class

Each instance of rdfs:Datatype is a subclass of rdfs:Literal


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Properties

Properties are instances of the class rdf :Property anddescribe a relation between subject resources and objectresources

rdfs :range is an instance of rdf:Property that defines thesuper-class of the values of a property

rdfs :domain is an instance of rdf:Property that is used todefine the super-class of the possible subjects for a given

property


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Properties

Example

The property #attends can be used in statements whose subject

belongs to the class #student and whose object belong to he class#course


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Containers

RDF containers are resources that are used torepresent collections

The rdfs :Container class is a super-class of the RDF

Container classes (discussed earlier) rdf:Bag

rdf:Seq

rdf:Alt

ll


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Collections

RDF containers are open The RDF Collection vocabulary of classes and properties can describe

a closed collection

A collection is represented as a list of items

rdf:List - used to build descriptions of lists and other list-likestructures (it is an instance of rdf:Class)

rdf:first (it is an instance of rdf:Property)

rdf:rest (it is an instance of rdf:Property)

rdf:nil (it is an instance of rdf:Property)

Sh SPARQL i l


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Short SPARQL tutorial

Plenty of resources and tutorial can be found on the web like on W3C siteand in http://www.cambridgesemantics.com/semantic-university/sparql-by-example

SPARQL queries data represented as an oriented graph: very different from

relational databases data model. Usage is simple but the approach of accessing a new data model can be

something hard the first times.

SPARQL 1.1 is in development, it will add many features to the original

specification. Some of its parts are currently supported by major semanticweb frameworks like Jena

The main resource to learn SPARL grammar is:http://www.w3.org/TR/rdf-sparql-query/#rGraphTerm

Short SPARQL tutorial
http://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-examplehttp://www.cambridgesemantics.com/semantic-university/sparql-by-example


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A SPARQL Query is pure text.

Queries can be classified in

SELECT ASK

CONSTRUCT

DESCRIBE

The SPARQL results set can be represented in XML by using the XML schema provided byW3C to wrap the results of SELECT and ASK queries

XML is not mandatory but often useful when representing results

The WHERE Clause


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The WHERE clause is the most important to be understood.

It contains an abstract description of a graph calledGroupGraphPattern in the official grammar description

Besides the operators defined on graphs is important to understandthat the basic expressive unit is that of the triples.

Triples are specified with subject, predicate and object separated byspaces

The WHERE Clause


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Triples are separated by .

There are shortcuts to express triples with recurring subjects orobject by using ; and ,

; after the subject tell that couples of predicates and objects willfollw, sharing the same subject

, after an object tell that another objects will follow sharing thesame subject and predicate

The WHERE Clause


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IRI are eclosed between

Qualified names does't need enclosing characters

Strings are double quoted other data types may be not, in general theliterals are represented in this way: quoted_literal^^IRI details

Details in the suggested internet address

SPARQL Examples


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Initial knowledge base:

Subject Predicate Object

http://ns#uri_0 http://ns#name Alfredo

http://ns#uri_0 http://ns#home http://ns/Alf_home.html

http://ns#uri_0 http://ns#role Adminhttp://ns#uri_0 http://ns#age 31

http://ns#uri_1 http://ns#name John

http://ns#uri_1 http://ns#role User

http://ns#uri_1 http://ns#age 44

SPARQL ExamplesSELECT ?a ?b ?c WHERE { ?a ?b ?c }


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SELECT ?a ?b ?c WHERE { ?a ?b ?c }

This query defines the variable a, b and c, which in the query must be

preceded by ? or $ and then specifies in the WHERE clause thegraph pattern against which all the triples will be matched, eachtriple matching the graph pattern is included in the results. In thiscase all the triples match so the result will be the entire data set, if wesuppose N stated triples:

a b c

http://ns#uri_0 http://ns#name Alfredo

http://ns#uri_0 http://ns#home http://ns/Alf_home.html

http://ns#uri_0 http://ns#role Admin





SPARQL Examples


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SELECT ?a WHERE { ?a ?b ?c } variables in the SELECT clause are theones included in the result set

a

http://ns#uri_0

http://ns#uri_0

http://ns#uri_0

http://ns#uri_0

http://ns#uri_1

http://ns#uri_1

http://ns#uri_1

SPARQL Examples


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The triples in the WHERE clause are considered in a conjunctive wayby default: SELECT ?a ?b ?c WHERE { ?a ?b ?c . ?a ?c}

a b chttp://ns#uri_0 http://ns#name Alfredo


SPARQL Examples


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Disjunction is obtained through the UNION pattern

SELECT ?a ?c WHERE { { ?a ?c } UNION { ?a ?c } }

a c

http://ns#uri_0 Alfredo

http://ns#uri_0 31

http://ns#uri_1 John

http://ns#uri_1 44

SPARQL ExamplesFiltering is used to restrict the admitted values of


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Filtering is used to restrict the admitted values ofliterals

SELECT ?a ?c WHERE { { ?a ?c }UNION { ?a ?c . FILTER regex(?c,John ) } }

Many filtering options available, readdocumentation for detail

a c

http://ns#uri_0 Alfredohttp://ns#uri_0 31


http://ns#uri_1 44

SPARQL Examples


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Optional patterns can be specified with the OPTIONALkeyword

SELECT ?a ?c ?d WHERE { { ?a ?c } UNION {?a ?c} . OPTIONAL { ?a ?d } }

a c d

http://ns#uri_0 Alfredo http://ns/Alf_home.html

http://ns#uri_0 31 http://ns/Alf_home.html


http://ns#uri_1 44

SPARQL Examples


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ASK queries are used to receive the information if at leastone solution exists for the specified patterns

ASK WHERE { { ?a ?c } UNION { ?a ?b } }

true

SPARQL Examples


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CONSTRUCT queries specifies at least two graph patterns: one is atemplate in which are present variables, like in a WHERE clause, butthe data set is not queried against this graph pattern. The second is anormal WHERE clause.

What happens is that the data are queried against the WHERE clauseand the value of the variables, for each solution, are substituted into

the template and the resulting graph (template with substitutedvalues) is returned as a query answer.

Construct { ?a ?c } WHERE { { ?c ?a }

SPARQL ExamplesDESCRIBE queries return an RDF graph representing a description of


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DESCRIBE queries return an RDF graph representing a description ofthe specified resource.

The description is built using the rules decided by the SPARQL endpoint manager, there is no standard defining it

DESCRIBE

http://ns#Alf_home.htmlAdmin31Alfredo

This is a possible response(by ARQ libraries)

SPARQL Examples


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DESCRIBE ?x WHERE { ?x ?y }

This is a possible response(by ARQ libraries)

User44John

http://ns/Alf_home.htmlAdmin

31Alfredo

SPARQL


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SPARQLOther samples

Subquery : a SPARQL 1.1 query feature (not standardized yet)Select ?a ?b where { ?a ?b . { Select ?a Where { ?a ?c } } }

a b

http://ns#uri_0 31

I want URI and age only for that URI with an associated home

SPARQL


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Aggregates and Groups : a SPARQL 1.1 query feature (not standardized yet)

We add to the knowledge base:

Select (SUM(STRLEN(?b)) as ?RolesLenght) where { ?a ?b } Having (SUM(STRLEN(?b)) >0 )

Select (SUM(STRLEN(?b)) as ?RolesLenght) where { ?a ?b } Group by ?bHaving ( SUM(STRLEN(?b)) >0 )

Q

Subject Predicate Object

http://ns#uri_2 http://ns#name Mark


RolesLenght

13The response is a single group of resultson which the functions STRLEN and SUMare Applied.

RolesLenght

8

5

The response is made up of as manygroups as the number of different roles.The STRLEN and SUM functions are

applied separately on each group

SPARQL


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QNegation:

Many possible approaches such as

OPTIONAL + !BOUND :Select ?a ?c Where { ?a ?c . Optional { ?a ?b } . Filter (!Bound(?b))

a c


http://ns#uri_2 Mark

I want URI and name only for that URI without an associated home.This solution is valid in standard SPARQL

Not exists:Select ?a ?c Where { ?a ?c . Filter not exists { ?a ?b } }

a c


http://ns#uri_2 Mark

Same objective and result, but with a feature of SPARQL 1.1 Querylanguage

SPARQL


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Q

In this short tutorial we will not investigate the support for other features ofSPARQL among them the named graphs for which clear documentation can befound in the main documentation page. This because SIB versions currently doesn'tsupport natively them, so it is difficult to verify in concrete applications during thecourse

http://www.w3.org/TR/rdf-sparql-query/

RDF Summary
http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/http://www.w3.org/TR/rdf-sparql-query/


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y

RDF Schema (RDFS) provides basic vocabulary for RDF RDF also allows for the re -use , extendibility and

refinement of established resource descriptionstandards since these will be available in machine -

readable form Using RDFS it is for example possible to create

hierarchies of classes and properties

RDF knowledge bases can be queried using the SPARQLlanguage.

Acknowledgments


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This tutorial is based on the material developedwithin RECOCAPE, an FP7 international cooperationproject of the capacities programme.

semantic web rdf website

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