Semantic Web for the Working Ontologist Dean Allemang Jim Hendler SNU IDB laboratory.
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Transcript of 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
3Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
4Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
5Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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8Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
10Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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12Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
1. Distributing Data across the Web: cell by cell
■ “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
13Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
1. Distributing Data across the Web: cell by cell
■ 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
Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
1. Distributing Data across the Web: cell by cell
Subject Predicate Object
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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15Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
16Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
17Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
18Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
3.1. Expressing URIs in Print
■ 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
Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
3.1. Expressing URIs in Print
Subject Predicate Object
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
3.2. Standard Namespaces
■ 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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
3.2. Standard Namespaces
■ 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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
4. Identifiers in the RDF Namespace
■ rdf:type
Provides an elementary typing system in RDF
■ Types can have types
Subject Predicate Object
lit:Shakespeare rdf:type lit:Playwrite
lit:Ibsen rdf:type lit:Playwrite
lit:Simon rdf:type lit:Playwrite
lit:Miller rdf:type lit:Playwrite
Subject Predicate Object
lit:Playwrite rdf:type lit:Profession
lit:Profession rdf:type lit:Compensation
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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
4. Identifiers in the RDF Namespace
■ rdf:Property
Identifier is used as a predicate rather than as a subject or an object
Subject Predicate 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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
5. Challenge: RDF and Tabular Data
Subject Predicate Object
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
5. Challenge: RDF and Tabular Data
Subject Predicate Object
mfg:Product1 rdf:type mfg:Product
mfg:Product2 rdf:type mfg:Product
mfg:Product3 rdf:type mfg:Product
mfg:Product4 rdf:type mfg:Product
… … …
mfg:Product8 rdf:type mfg:Product
mfg:Product9 rdf:type mfg:Product
Triples Representing Type of Information
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27Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
■ “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
6. Higher-Order Relationships
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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
6. Higher-Order Relationships
■ “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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30Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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
Subject Predicate Object
lit:Shakespeare lit:wrote lit:KingLear
Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
7.2. Notation 3 RDF (N3)
■ 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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
7.2. Notation 3 RDF (N3)
■ 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 rdf:type mfg:Product.
mfg:Product1 mfg:Product_Division “Manufacturing support”.
mfg:Product1 mfg:Product_Available “23”.
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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
7.2. Notation 3 RDF (N3)
■ 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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
7.2. Notation 3 RDF (N3)
■ Abbreviation
a means rdf:type
mfg:Product1 rdf:type mfg:Product.
mfg:Product1 a mfg:Product.
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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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Semantic Web for the Working Ontologist Dean Allemang, Jim Hendler
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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