What is RDF? Don Tonkin, Semantic Software Asia Pacific. Session Code: 4013 Friday, Sep 18, 2015 (08:30 AM - 09:30 AM) Platform: Analytics

(1)

What is RDF ?

Don Tonkin,

Semantic Software Asia Pacific

Session Code: 4013

Friday, Sep 18, 2015 (08:30 AM - 09:30 AM) Platform: Analytics

(2)

Agenda

RDF is an emerging technology for storing data. It introduces a new query language SPARQL. Both are supported by DB2 10.0+. This is a beginner’s

introduction to RDF and its related technologies

• Objectives

• History of Data Science

• Definition of RDF and an RDF Store

• The RDF Schema and Ontologies

• Query an RDF store using SPARQL

2

(3)

Don Tonkin

Semantic Software Asia Pacific

[email protected]

What is RDF ?

Please fill out your session evaluation before leaving!

(4)

Objectives

By the end of this session you will

• Know that RDF, RDFS, SPARQL and Ontologies exist

• Have a vague idea of how they are structured

• Have some concepts of how they are used

• Have a burning desire to know more!

4

(5)

The History of Data Science

A Bowdlerised Version

The highlights in the evolution of Data Science are:

• 1822 Babbage Difference engine – Field manipulation

• 1890 Hollerith punched cards – Record manipulation

• 1959 Sputnik

• 1960 IBM IMS – Hierarchical Database

• 1960-1980 – various empirically designed databases

• 1970 Codd Relational Theory – Relational Database

• 1996 XML – Data with structure and metadata

• 2002 RDF – AAA: Anyone can say anything about anything

(6)

The History of Data Science

Web Evolution

6

(7)

The History of Data Science

Hype Cycle

Source: http://www.gartner.com/newsroom/id/2819918?_ga=1.51071721.1904172021.1401730474

(8)

8

Definition of RDF and an RDF Store The Data Problem

How to manage -

• Structured Data

• Can be normalised

• Unstructured Data

• No data model etc

• Semi-structured Data

• Meta-data tags

(9)

Definition of RDF and an RDF Store

New Terminology

URI IRI RDF

Linked data SPARQL

Data Silo Triplestore

– uniform resource identifier

– resource description framework – shared connected data

– RDF query language

– high volume non-interoperable – international resource identifier

– triples database

(10)

Definition of RDF and an RDF Store

Basic Ideas of RDF

• RDF is a universal language that lets users

describe resources in their own vocabularies

• RDF does not assume, nor does it define semantics of any particular application domain

• The user can do so in RDF Schema using:

• Classes and Properties

• Class Hierarchies and Inheritance

• Property Hierarchies

• Each item qualified by a URI

(11)

Definition of RDF and an RDF Store

RDF Statement Rules

Subject Predicate Object

Statement 1 p1 type Person Statement 2 p1 name John Smith

Statement 3 p1 email [email protected]

• expressed as a triple

• subjects, predicates, and objects are named entities

• objects can be literals

An RDF graph is a set of RDF triples

• Subject/Predicate/Object

• Triples are statements (i.e. they are true or false)

• The smallest graph is a single triple

(12)

Definition of RDF and an RDF Store

RDF Graph

12

Subject Predicate Object

The Lord of the Rings Is Written By J.R.Tolkein The Lord of the Rings Is a Book

Resource Property Literal Value

Resource

The Lord of The Rings

J.R.Tolkein Is Written By

Book

(13)

Definition of RDF and an RDF Store

RDF Example

•Subject : "Lord of the Rings“

<

http://dbpedia.org/page/The_Lord_of_the_

Rings

^>

•Predicate : "Is written by"

<

http://dbpedia.org/ontology/author

^>

•Object : "J.R.R Tolkien"

<http://dbpedia.org/page/J._R._R._Tolkien>

Data structure but not the semantics

13

(14)

Definition of RDF and an RDF Store

RDF / xml Language (One of Many variants)

14

<?xml version="1.0"?>

<rdf:RDF

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:cd="http://www.recshop.fake/cd#">

<rdf:Description

rdf:about="http://www.recshop.fake/cd/Empire Burlesque">

<cd:artist>Bob Dylan</cd:artist>

<cd:country>USA</cd:country>

<cd:company>Columbia</cd:company>

<cd:price>10.90</cd:price>

<cd:year>1985</cd:year>

</rdf:Description>

</rdf:RDF>

XML declaration RDF root

Description of “about”

End RDF statement End Description Description

Name space Name space

Resource Resource Resource Resource

Resource

(15)

The RDF Schema and Ontologies

RDF Schema

<?xml version="1.0"?>

<rdf:RDF

xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"

xmlns:rdfs="http://www.w3.org/2000/01/rdf-schema#"

xml:base="http://www.animals.fake/animals#">

<rdfs:Class rdf:ID="animal" />

<rdfs:Class rdf:ID="horse">

<rdfs:subClassOf rdf:resource="#animal"/>

</rdfs:Class>

</rdf:RDF>

(16)

The RDF Schema and Ontologies

RDF Schema Components

16

(17)

OWL XSD XML/N3

RDFS RDF

Triple and URI Single fact Additional structure Defines classes and

relationships File format Describes property types Adds meaning, allows inferencing

John hasA dog Boolean, integer

Reasoners, synonyms

Subclasses Types

Turtle

The RDF Schema and Ontologies

Semantic Web Layers

(18)

18

who how where why what when access

Provenance Information in the Web of Data Olaf Hartig 2009

The RDF Schema and Ontologies

Provenance Data

(19)

The RDF Schema and Ontologies

Web Ontology Language - OWL

• describes relationships

• XML

• on RDF

• on the web

• understood by computers

• not for people

• W3C standard

(20)

The RDF Schema and Ontologies

OWL Components

20

Class and individual elements

• owl:Class

• owl:Thing

• owl:Nothing

• owl:Namedlndividual

RDFS elements used in OWL

• rdfs:subClassOf

• rdf:Property

• rdfs:subPropertyOf

• rdfs:domain

• rdfs:range

Datatype specification

• xsd:datatypes

Property characteristics

• owl:ObjectProperty

• owl:DataProperty

• owl:inverseOf

• owl:TransitiveProperty

• owl:SymmetricProperty

• owl:FunctionalProperty

• owl:InverseFunctionalProperty

• Cardinality restrictions

• owl:minCardinality

• owl:rnaxCardinality

• owl:cardinality

(21)

The RDF Schema and Ontologies

OWL Components - 2

Equality/inequality

• owl:equivalentClass

• owl:equivalentProperty

• owl:sameAs

• owl:differentFrom

• owl:AllDifferent

• owl:distinctMembers

Property restrictions

• owl:Restriction

• owl:onProperty

• owl:all ValuesFrom

• owl:someValuesFrom

Class intersection

• owl:intersectionOf

OWL DL & OWL Full:

Class axioms

• owl:one of, dateRange

• owl:disjointWith

• owl:equivalentClass

(applied to class expressions)

• rdfs:subClassOf

(applied to class expressions)

Boolean combinations of class expressions

• owl:unionOf

• owl:complementOf

• owl:intersectionOf

Property information

• owl:hasValue

(22)

The RDF Schema and Ontologies

Ontology v Database Schema

22

ONTOLOGY Focus on Meaning Data Instances

• optional

Axioms

• meaning and context

Comments

• contained within

Change

• flexible

Ambiguity

• frequent

DATABASE SCHEMA Focus on Data

Data Instances

• fundamental

Database Constraints

• data integrity

Metadata Repository

• separate Entity

Change

• rigid and slow

Ambiguity

• rare

(23)

The RDF Schema and Ontologies

Semantic Data v Relational Data

SEMANTIC DB

• Meaning of Information is Stored

• Relationship Between Classes

• No Restriction on Data Type/Size

• Any Query Can be Run Ad Hoc

 Any Relation Can be Viewed

• No Keys are Required

RDBMS

• Meaning of Information is not captured

• Relationships not Supported

• Restricted Data Types and Sizes

• Many Queries Have to be Predicted

 “Joins” are frequently Needed

• Keys are Required and are Static

(24)

The RDF Schema and Ontologies

Ontologies

• There are public ontologies for thousands of subject areas

• Finance

• Medicine

• Real Estate

• Geospatial

• There are tools for managing ontologies

• Creating and editing

• Pruning

• Aligning

• Visualising

24

(25)

The RDF Schema and Ontologies

Benefits of RDF

• Graph modelling is flexible

• Adding/removing a new edge or vertex is simple

• Adding an edge is like adding a new column to a table but easier

• Standard based graph representation

• RDF was defined by W3C. Allows interoperability

• Computers can understand the semantics RDF graphs

• Discover hidden relationships via inferencing

• Same URI means same resource

• Data integrated over multiple disciplines

(26)

The RDF Schema and Ontologies

Data Integration Example

26

(27)

Query an RDF store using SPARQL

SPARQL Protocol and RDF Query Language

SPARQL (SPARQL Protocol and RDF Query Language) is

• W3C standard for querying and manipulating RDF content

• Queries may consist of triple patterns, conjunctions, disjunctions, and optional patterns

• Queries/updates and corresponding results are communicated via HTTP with a SPARQL endpoint

• A SPARQL endpoint implements the SPARQL protocol and serves RDF data from a RDF triplestore or RDF view

(28)

Query an RDF store using SPARQL

SPARQL Components

Four query variations

1. SELECT query. Extracts raw values from a SPARQL endpoint, the results in table format

2. CONSTRUCT query. Extracts information from the SPARQL endpoint and transforms the results into valid RDF

3. ASK query. Provides a simple True/False result for a query on a SPARQL endpoint

4. DESCRIBE query. Extracts an RDF graph from the SPARQL endpoint

28

(29)

Query an RDF store using SPARQL

SPARQL Examples

SPARQL query

"What are all the country capitals in Africa?":

PREFIX ex: <http://example.com/exampleOntology#>

SELECT ?capital ?country

WHERE { ?x ex:cityname ?capital ; ex:isCapitalOf ?y . ?y ex:countryname ?country ; ex:isInContinent ex:Africa . }

(30)

Query an RDF store – Find all persons

30

(31)

Query an RDF store – Find Alice

(32)

Query an RDF store - Recurse who Alice knows

32

(33)

Query an RDF store – Find who Alice doesn’t know

(34)

Query an RDF store using SPARQL

SPARQL 1.1 Update: INSERT DATA

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

PREFIX my: <http://www.mydomain.com/>

INSERT DATA

{ my:person1 foaf:name “Don Tonkin" . my:person1 foaf:gender “male”}

PREFIX foaf: <http://xmlns.com/foaf/0.1/>

PREFIX my: <http://www.mydomain.com/>

INSERT { ?p foaf:worksFor “IBM Australia" } WHERE { ?p foaf:worksFor “IBMA" }

34

(35)

Query an RDF store using SPARQL

:res1 rdf:type :House .

:res1 :baths "2.5"^^xsd:decimal . :res1 :bedrooms "3"^^xsd:decimal .

:res2 rdf:type :Unit .

:res2 :baths "2"^^xsd:decimal . :res2 :bedrooms "2"^^xsd:decimal .

:res3 rdf:type :House

:res3 :baths "1.5"^^xsd:decimal . :res3 :bedrooms "3"^^xsd:decimal .

RDF Data SELECT ?r ?ba ?br

WHERE { ?r rdf:type :House .

?r :baths ?ba .

?r :bedrooms ?br FILTER (?ba > 2) }

?r | ?ba | ?br

===================

:res1 | "2.5" | "3"

(36)

Query an RDF store using SPARQL

:res1 rdf:type :House .

:res1 :baths "2.5"^^xsd:decimal . :res1 :bedrooms "3"^^xsd:decimal . :res1 ogc:hasGeometry :geom1 . :geom1 ogc:asWKT "POINT(151.21, - 33.85)"^^ogc:wktLiteral .

:res3 rdf:type :House

:res3 :baths "1.5"^^xsd:decimal . :res3 :bedrooms "3"^^xsd:decimal . :res3 ogc:hasGeometry :geom3 . :geom3 ogc:asWKT " POINT(149.10, - 35.35)"^^ogc:wktLiteral .

36

RDF Data SELECT ?r ?ba ?br

WHERE { ?r rdf:type :House .

?r :baths ?ba .

?r :bedrooms ?br FILTER (?ba > 2) }

Add spatial terms such as

• Distance

• Within area

• Touches

?r | ?ba | ?br

===================

:res1 | "2.5" | "3"

(37)

Query an RDF store using SPARQL

• Extremely complex queries are possible

• SPARQL queries can be imbedded in SQL statements

• Vendor specific functions at this stage

• Integration with analytics tools

(38)

Conclusions

RDF:

• allows integration of structured and unstructured data

• provides mechanism for ‘Big Data’ management

• Ontologies and data models differ

• Consistency but not completeness

• Integration challenges

• Data ambiguity is a challenge

• Semantic processing is increasing

• NLP is a key component

38

(39)

Query an RDF store using SPARQL Some examples

• An example of a Triple Store http://dbpedia.org/page/London

• Some Ontologies

http://protegewiki.stanford.edu/wiki/Protege_Ontology_Libra ry

• Relationship Finder

http://www.visualdataweb.org/relfinder/relfinder.php