semantic web for the working ontologist dean allemang jim hendler snu idb laboratory

Semantic Web for the Working Ontologist

Dean Allemang

Jim Hendler

SNU IDB laboratory

2Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler

Working Ontology Contents

■ Chapter 1 What is the Semantic Web?

■ Chapter 2 Semantic Modeling

■ Chapter 3 RDF-The Basis of the semantic Web

■ Chapter 4 Semantic Web Application Architecture

■ Chapter 5 RDF and Inferencing

■ Chapter 6 RDF Schema

■ Chapter 7 RDFS-Plus

■ Chapter 8 Using RDFS-Plus in the Wild

■ Chapter 9 Basic OWL

■ Chapter 10 Counting and Sets in OWL

■ Chapter 11 Using OWL in the Wild

■ Chapter 12 Good and Bad Modeling Practices

■ Chapter 13 OWL Levels and Logic


Chapter 3 RDF – The Basis of the Semantic Web

■ 1. Distributing Data Across the Web

■ 2. Merging Data from Multiple Sources

■ 3. Namespaces, URIs, and Identity

3.1. Expressing URIs in Print

3.2. Standard Namespaces

■ 4. Identifiers in the RDF Namespace

■ 5. Challenge: RDF and Tabular Data

■ 6. Higher-Order Relationships

■ 7. Alternatives for Serialization

7.1. N-Triples

7.2. Notation 3 RDF (N3)

7.3. RDF/XML

■ 8. Blank Nodes

8.1. Ordered Information in RDF


Introduction: Semantics

■ The most primitive part of this notion of semantics

is a representation of the linkage of a term in a statement to the entity in the world that the term refers to

apple

Real WorldWeb


Introduction: Semantics

■ In the Semantic Web we refer to the things in the world as resources

■ Resource ≈ Entity, Thing

Can be anything that someone might want to talk about

■ RDF = Resource Description Framework

resource

resource

resource

RDF

Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler

1. Distributing Data across the Web

ID Title Author Medium Year

1 As You Like It Shakespeare Play 1599

2 Hamlet Shakespeare Play 1604

3 Othello Shakespeare Play 1603

4 “Sonnet 78” Shakespeare Poem 1609

5 Astrophil and Stella Sir Phillip Sidney Poem 1590

6 Edward ll Christopher Marlowe Play 1592

7 Hero and Leander Christopher Marlowe Poem 1593

8 Greensleeves Henry Vlll Rex Song 1525

Tabular Data about Elizabethan Literature and Music

Let’s consider a few different strategies for how this data could be distributed over the Web!

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1. Distributing Data across the Web: row by row

1 As You Like It Shakespeare Play 1599

5 Astrophil and Stella Sir Phillip Sidney Poem 1590

6 Edward ll Christopher Marlowe Play 1592

7 Hero and Leander Christopher Marlowe Poem 1593

8 Greensleeves Henry Vlll Rex Song 1525

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1. Distributing Data across the Web: row by row

■ “row by row” distribution solution provides considerable flexibility

Since the machines can share the load of representing information about several individuals

But because it is a distributed representation of data, it requires some coordi-nation between the servers

■ In particular, each server must share information about the columns

Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler9

1. Distributing Data across the Web: column by column

Title

As You Like It

Hamlet

Othello

“Sonnet 78”

Astrophil and Stella

Edward ll

Hero and Leander

Greensleeves

Author

Shakespeare

Shakespeare

Shakespeare

Shakespeare

Sir Phillip Sidney

Christopher Marlowe

Christopher Marlowe

Henry Vlll Rex

Medium Year

Play 1599

Play 1604

Play 1603

Poem 1609

Poem 1590

Play 1592

Poem 1593

Song 1525


1. Distributing Data across the Web: column by column

■ “row by row” distribution solution (also flexible in a different way)

Each server is responsible for one or more complete from original table

If we are not interested in the dates of publication, we needn’t consider infor-mation from that server

■ It requires some coordination between the servers

The coordination has to do with the identities of the entities to be described

It requires a global identifier for the entities being described


1. Distributing Data across the Web: cell by cell

Medium

Row 7 Poem

Medium

Row 6 Play

Title

Row 2 Hamlet

Author

Row 4 Shakespeare

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■ “cell by cell” distribution solution (this strategy is taken by RDF)

Each machine is responsible for some number of cells in the table

This system combines the flexibility of both of the previous strategies (row by row + column by column)

Share the description of a single entity (row by row) + Share the use of a par-ticular property (column by column)

■ But this solution also combines the costs of the other two strategies

Need a global reference for the column headings

Need a global reference for the rows



■ Each cell has to be presented with three values Triple

A global reference for the row

A global reference for the column

Value in the cell it self

■ Basic building block for RDF is triple

Identifier for the row is subject of the triple

Identifier for the column is predicate of the triple

Value is object of the triple

Subject Predicate Object

Row 2 Title Hamlet

Row 7 Medium Poem

Row 4 Author Shakespeare

Row 6 Medium Play




Shakespeare Wrote King Lear

Shakespeare Wrote Macbeth

Anne Hathaway Married Shakespeare

Shakespeare Lived in Stratford

Stratford Is in England

Macbeth Set in Scotland

England Part of The UK

Scotland Part of The UK

Shakespeare

Macbeth

Stratford

England

King Lear

Anne Hathaway

Sample TriplesScotlan

d

UK

married

wrote

wrote

lived in

set in

is in

part ofpart of

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2. Merging Data from Multiple Sources

■ Section 1: a way to distribute data over several sources

■ Section 2: merge those sources back together again

Triples representation is easy to merge

Taken together all of the triples from each individual RDF graph

UKEnglan

d

Northern Ireland

Wales

Scotland

Shakespeare

Winter Tale

Henry V

The Tempest

Macbeth

King Lear part of

part of

part of

part of

wrote

wrote

wrote

wrote

wrote


2. Merging Data from Multiple Sources

UK

England

Northern Ireland

Wales

Scotland

Shakespeare

Winter Tale

Henry V

The Tempest

Macbeth

King Lear

part of

part of

part of

part of

wrote

wrote

wrote

wrote

wrote

Stratford

LivedIn

IsIn

setIn


3. Namespaces, URIs, and Identity

“When is a node in one graph the same node as a node in another graph?”

■ In RDF, Uniform Resource Identifiers (URIs)

A URI provides a global identification for a resource

URL is just a special case of the URI

Shakespeare

King Lear

wrote

Http://www.sample.com/shakespeare.owl#Shakespeare

Http://www.sample.com/shakespeare.owl#wrote

Http://www.sample.com/shakespeare.owl#KingLear

Shakespeare wrote KingLear



■ URI work very well for expressing identity on the WWW

But it is too detail, long..

■ So we use a simplified version of a URI abbreviation scheme called qnames

A namespace and an identifier written with a colon

Qnames are not global identifiers

Http://www.sample.com/geography.owl#England

geo:England




lit:Shakespeare lit:wrote lit:KingLear

lit:Shakespeare lit:wrote lit:Macbeth

bio:AnneHathaway bio:married lit:Shakespeare

bio:AnneHathaway bio:livedWith lit:Shakespeare

lit:Shakespeare bio:livedIn geo:Stratford

geo:Stratford geo:isIn geo:England

geo:England geo:part of geo:UK

geo:Scotland geo:partOf geo:UK

Triples Referring to URIs with a Variety of Namespaces

lit stands for http://www.WorkingOntologist.org/Examples/Chapter3/Shakepeare.owl#geo stands for http://www.WorkingOntologist.org/Examples/Chapter3/geography.owl#bio stands for http://www.WorkingOntologist.org/Examples/Chapter3/biography.owl#

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■ Using the URI as a standard for global identifiers allows for a worldwide refer-ence for any symbol

■ W3C standards provide definitions for terms

ex) type, subClassOf, Class, inverseOf, …

■ W3C defined standard namespaces

ex) xsd: XML schema definition

xmlns: XML namespace..

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■ rdf:

Indicates identifiers used in RDF

Set of identifiers is used to define types and properties in RDF

Http://www.w3.org/1999/02/22-rdf-syntax.ns#

■ rdfs:

Indicates identifiers used for the RDF Schema Language

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

■ owl:

Indicates identifiers used for the Web Ontology Language

Http://www.w3.org/2002/07/owl#

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4. Identifiers in the RDF Namespace

■ rdf:type

Provides an elementary typing system in RDF

■ Types can have types


lit:Shakespeare rdf:type lit:Playwrite

lit:Ibsen rdf:type lit:Playwrite

lit:Simon rdf:type lit:Playwrite

lit:Miller rdf:type lit:Playwrite


lit:Playwrite rdf:type lit:Profession

lit:Profession rdf:type lit:Compensation

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4. Identifiers in the RDF Namespace

■ rdf:Property

Identifier is used as a predicate rather than as a subject or an object


lit:wrote rdf:type rdf:Property

geo:part of rdf:type rdf:Property

bio:married rdf:type rdf:Property

bio:livedIn rdf:type rdf:Property

bio:livedWith rdf:type rdf:Property

geo:Isin rdf:type rdf:Property

rdf:Property Assertions

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5. Challenge: RDF and Tabular Data

■ ID is a locally unique identifier

■ We need a globally unique identifier

■ Let us call that namespace mfg:

■ Identifiers

ex) mfg:Product1, mfg:Product2, …

■ Properties

ex) mfg:Product_ModelNo, mfg:Proudct_Division, …

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mfg:Product1 mfg:Product_ID 1

mfg:Product1 mfg:Product_ModelNo ZX-3

mfg:Product1 mfg:Product_Division Manufacturing Support

mfg:Product1 mfg:Product_Product_Line Paper Machine

mfg:Product1 mfg:Product_Manufacture_Location Scramento

mfg:Product1 mfg:Product_SKU FB3524

mfg:Product1 mfg:Product_Available 23

mfg:Product2 mfg:Product_ID 2

… … …

Triples Representing Some of the Data

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mfg:Product1 rdf:type mfg:Product




… … …



Triples Representing Type of Information

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6. Higher-Order Relationships

■ Reification

In general, there are cases in which it is desirable to make a statement about another statement

This process called reification

Shakespeare wrote Hamlet

Shakespeare wrote Hamlet in 1604

Wikipedia states Shakespeare wrote Hamlet in 1604


■ “Shakespeare wrote Hamlet in 1601” can be expressed with three triples

bio:n1 bio:author lit:Shakespeare;

bio:title “Hamlet”;

bio:publicationDate 1601.

■ This approach works well in this case

■ But, it doesn’t work to express information about the statement itself

“Wikipedia says Shakespeare wrote Hamlet”

■ Explicit reification

In such cases, it is useful to explicitly make a statement about a statement


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■ “Wikipedia says Shakespeare wrote Hamlet”

q:n1 rdf:subject lit:Shakespeare;

rdf:predicate lit:wrote;

rdf:object lit:Hamlet.

web:Wikipedia m:says q:n1.

■ Explicit reification is supported by the W3C RDF standard with rdf:subject, rdf:predicate, and rdf:object

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7. Alternatives for Serialization

■ So far, we have expressed RDF triples in subject/predicate/object tabular form or as graphs of boxes and arrows

■ But they are not always the most compact forms

■ So, there are multiple ways of expressing RDF in textual form

N-Triples

Notation 3 RDF (N3)

RDF/XML

Shakespeare

King Lear

wrote


lit:Shakespeare lit:wrote lit:KingLear


7.1. N-Triples

■ N-triples

Corresponds most directly to the raw RDF triples

Using fully unabbreviated URIs

Three resources are expressed in subject/predicate/object order

<http://www.WorkingOntologist.org/Examples/Chater3Manufacture.rdf#Product1>

<http://www.w3.org/1992/02/22-rdf-syntax-ns#type>

<http://www.WorkingOntologist.org/Examples/Chapter3Manufacture.rdf#Product>

N-triples

Product1

Product

type

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■ Notation 3 RDF (N3)

More compact serialization of RDF

Binding between the local qnames an the global URIs

N3 provides a compact representation

@prefix mfg:<http://www.WorkingOntologist.org/Examples/Chapter3/Manufacturing.rdf#>

@prefix rdf:<http://www.w3.org/1999/02/22-rdf-syntax-ns#>

mfg:Product1 rdf:type mfg:Product.

N3

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■ N3 begins with the first triple in subject/predicate/ object order

■ A semicolon (;) indicates that another triple with the same subject follows

■ Terminating with a period (.)

mfg:Product1 rdf:type mfg:Product;

mfg:Product_Division “Manufacturing support”;

mfg:Product_Available “23”.


mfg:Product1 mfg:Product_Division “Manufacturing support”.

mfg:Product1 mfg:Product_Available “23”.

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■ Several triples share both subject and predicate

N3 uses a comma (,) to separate the objects

lit:Shakespeare b:hasChild b:Susanna, b:Judith, b:Hamlet.

lit:Shakespeare b:hasChild

b:Susanna.

lit:Shakespeare b:hasChild b:Judith.

lit:Shakespeare b:hasChild b:Hamlet.

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■ Abbreviation

a means rdf:type


mfg:Product1 a mfg:Product.

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7.3. RDF/XML

■ W3C has recommended the use of an XML serialization of RDF called RDF/XML

(Many web infrastructures are accustomed to representing information in XML)

<rdf:RDF xmlns:mfg=“http://www.WorkingOntologist.org/Examples/Chapter3/Manufacturing.rdf#” xmlns:rdf=“http://www.w3.org/1999/02/22-rdf-syntax-ns#> <mfg:Product rdf:about=“http://www.WorkingOntologist.org/Examples/Chapter3/Manufacturing.rdf# Product1”> <mfg:Available>23</mfg:Available> <mfg:Division>Manufactuingsupport</mfg:Division> <mfg:ProductLine>Paper machine</mfg:ProductLine> <mfg:SKU>FB3524</mfg:SKU> <mfg:ModelNo>ZX-3</mfg:ModelNo> <mfg:ManufactureLocation>Sacramento</mfg:ManufactureLocation> </mfg:Product> …</rdf:RDF>

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8. Blank Nodes

■ RDF allows for resource that do not have any Web identity at all

■ Example: “Shakespeare had a mistress”

■ Her identity remains unknown

But we know a few things about her

▶ She was a woman

▶ She lived in England

▶ She was the inspiration for “Sonnet 78”

lit:Mistress1 rdf:type bio:Woman; bio:LivedIn geo:England .

lit:Sonnet78 lit:hasInspiration lit:Mistress1.

∵ Her identity remains unknown

? rdf:type bio:Woman; bio:LivedIn geo:England .

lit:Sonnet78 lit:hasInspiration ? .

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8. Blank Nodes

■ RDF allows blank node (bnode for short)

■ But this notation can not express more than one blank node

■ In N3, a bnode is indicated by putting all the triples between square brackets

A blank node is referred by including the entire bracketed sequence in place of the blank node

? rdf:type bio:Woman; bio:LivedIn geo:England .

lit:Sonnet78 lit:hasInspiration ? .

lit:Sonnet78 lit:hasInspiration [ a bio:Woman;

bio:livedIn England;

… ] .

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8.1. Ordered Information in RDF

■ An ordered list can be expressed in N3 as follows

lit:Shakespeare b:hasChild ( b:Susanna b:Judith b:Hamlet) .

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semantic web for the working ontologist dean allemang jim hendler snu idb laboratory

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