1. The Vision and Basic Technologies of the Semantic Web.
The Semantic Web – Part 1
Lecturer
Organization
Date of presentation
The Vision and Basic Technologies of the Semantic Web.
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2. Part III: Methodologies
Part II: Semantic
Content Management
Part III: Methodologies
Knowledge Interaction and Presentation
Designing Interactive Ubiquitous IS
Knowledge Representation and Reasoning
Semantifying your CMS
Semantic Lifting
Reference Architecture for Semantic CMS
Storing and Accessing Semantic Data
Requirements Engineering for Semantic CMS
Part I: Foundations
Content Management
The Semantic Web
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3. What is this Lecture about?
Semantic web technologies as a possible solution for improving the „state of play“ in content management by making semantics expressable in machine-readable way
The Semantic Web
The vision behind the semantic web
Underlying technologies of the Semantic Web
Part I: Foundations
Content Management
The Semantic Web
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4. Web Engineering WT 2006/07 Chapter 4: Web Services
Web evolution
Web 3.0
Web 4.0
A digital library (1.0, the Web of Documents)
A document library with hyperlinks
A database, an application platform (1.0, evolved)
A shared portal through which applications can be web accessible
A multimedia and social platform (2.0, the Social Web)
A radio, a trailer, a telephone, a tv, a public place, a position anywhere in the world. Collaboration, “web editing”
A naming scheme (3.0, the Web of Data)
Unique identity for all entities: documents, persons, services, physical things, metadata, ...
URI-based data integration is the key use-case for the semantic web
A Global Giant Graph (4.0. the actual Semantic Web)
A place where people work, interact, and produce interpretations assisted by computers
Web 2.0
Web 1.0
Slide by Nova Spivack, Radar Networks
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© Gregor Engels University of Paderborn

5. The Semantic Web
The vision of the Semantic Web has been originally proposed by Tim Berners-Lee
“The Semantic Web is not a separate Web but an extension of the current one, in which information is given well-defined meaning, better enabling computers and people to work in cooperation.” [The Semantic Web, 2001]
Standardized specification techniques for the semantic annotation of content (RDF, OWL, ...)
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6. Semantic Web Stack
W3C provides standardized specifications for Semantic Web technologies
Semantic Web Layer Cake as a conceptual architecture describes an hierarchy of languages
Each layer exploits and uses capabilities of the layers below
Semantic Web Layer Cake, Image source:
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7. Unique Identification of Resources
“...more fundamental than either HTTP or HTML are URIs, which are simple text strings that refer to Internet resources -- documents, resources, people, and indirectly to anything. URIs are the glue that binds the Web together. IRIs extend and strengthen the glue, by allowing people to identify Web resources
in their own language.”
In a “Web of Data” the unique
identification of entities is required
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8. How to identify resources?
Web Engineering WT 2006/07 Chapter 4: Web Services
How to identify resources?
URI – Uniform Resource Identifier [RFC 3986]
“A Uniform Resource Identifier (URI) is a compact sequence of characters that identifies an abstract or physical resource.”
A URI consists of five parts: scheme, authority, path, query and fragment
URI = scheme ":" authority "/" path [ "?" query ] [ "#" fragment ]
Example:
scheme
authority
path
query
fragment
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© Gregor Engels University of Paderborn

9. How to identify resources?
IRI – Internationalized Resource Identifier [RFC 3987]
“IRIs are defined similarly to URIs in [RFC3986], but the class of unreserved characters is extended by adding the characters of the UCS (Universal Character Set, [ISO10646]) ..”
Extends the character set used by URIs and thereby allows the consideration of language specific syntaxes (e.g. Japanese, Chinese, ...)
Example
Logical Hebrew
ASCII notation
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10. Structuring Data XML – Extensible Markup Language
XML can be used to specify the syntactical structure of documents or complex data objects in a machine-readable form
<car>
<brand>Jaguar</brand>
<model>XF</model>
<dimensions>
<length>4961</length>
<width>2070</width>
</dimensions>
<engine>5.0 L V8 Petrol</engine>
</car>
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11. The difference in meaning is only recognized by a human.
Why isn´t XML enough?
XML tags are only defining the structure of a document
For a machine the tags have no semantics!
<car>
<brand>Jaguar</brand>
...
</car>
<cat>
<brand>Jaguar</brand>
...
</cat>
The difference in meaning is only recognized by a human.
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12. Why isn´t XML enough?
The relation among the different tags is not expressed explicitly
<car>
<brand>Jaguar</brand>
...
</car>
The relation between “car”, “brand” and “Jaguar” is only recognizable by a human.
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13. What do we need? We want to express the statement: We need ...
“The brand of the car is Jaguar.”
We need ...
...a way to address the concrete resource car.
... to express the property brand of the resource car.
... to define the property value Jaguar for the property brand.
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14. Resource Description Framework (RDF)
“The Resource Description Framework (RDF) identifies things using Web identifiers (URIs), and describes resources with properties and property values.”
A Resource is an object that can be identified by an URI, e.g. “
A Property describes an aspect of a resource, e.g. “ The property is also identified by an URI.
The Property value assigns a concrete value to a property, e.g. “Jaguar” or ““
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15. RDF Statements
RDF statements consist of subject (resource), predicate (property) and object (property value)
Subjects (except Blank Nodes) and Predicates are always defined by URIs
Objects can be defined by URIs and literals
Predicate
Subject
Object
(URI)
Predicate
Object (literal)
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16. RDF Statements - Example
Exemplary statements:
“The brand of the car is Jaguar.”
“The model of the car is XF.”
Subject
Predicate
Object XF
Predicate
Object
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17. Resource Description Framework (RDF)
“The Resource Description Framework (RDF) is a language for representing information about resources...” [RDF Primer]
W3C Standard (
RDF provides a graph-based data model
for representing metadata
for describing the semantics of
information in a machine-accessible way
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18. RDF Serialization Formats
RDF/XML N3
N-Triples
TRiG
TRiX
Turtle
JSON
JSON-LD
RDFa
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19. RDF/XML
RDF/XML is the most common serialization format for RDF statements
Example:
<rdf:RDF xmlns:rdf="
xmlns:rel="
<rdf:Description rdf:about="
<rel:Brand rdf:resource="
</rdf:Description>
<rel:Model>XF</rel:Model>
</rdf:RDF>
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20. Root Element and Namespaces
Root element of the RDF/XML document.
<rdf:RDF
xmlns:rdf="
xmlns:rel="
....
</rdf:RDF>
Defined namespaces
<rdf:RDF>
Root element of RDF documents
xmlns:rdf
Specifies that elements with the “rdf” prefix are using the namespace “..”
xmlns:abc
Specifies that elements with the “abc” prefix are using the namespace “..”
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21. Description Element Node element Assigns a resource to
<rdf:RDF xmlns:rdf="
xmlns:rel="
<rdf:Description rdf:about="
...
</rdf:Description>
</rdf:RDF>
Assigns a resource to
the node element.
<rdf:Description>
Introduces node element (subject).
<rdf:about>
Defines the URI reference for the node element.
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22. Objects defined by Resources
Assigning resources to objects (property values) in RDF/XML
<rdf:RDF xmlns:rdf="
xmlns:rel="
<rdf:Description rdf:about="
<rel:Brand rdf:resource="
</rdf:Description>
</rdf:RDF>
Defines predicate “Brand” in namespace “rel”.
The object is defined
by a resource.
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23. Objects defined by Literals
Definition of objects (properties) with constant values (literals)
<rdf:RDF xmlns:rdf="
xmlns:rel="
<rdf:Description rdf:about="
<rel:Model>XF</rel:Model>
</rdf:Description>
</rdf:RDF> XF
The object is defined
by a literal.
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24. RDF Container Elements
“A container is a resource that contains things. The contained things are called members. The members of a container may be resources (including blank nodes) or literals.”
Container provide the ability to describe groups of things, e.g. several authors of a book
RDF defines three types of containers:
Bag
Sequence
Alternatives
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25. Container Element - Bag
“A Bag (a resource having type rdf:Bag) represents a group of resources or literals, possibly including duplicate members, where there is no significance in the order of the members.”
Example:
Describe equipment features of the car.
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26. Container Element - Bag
Blank Node
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27. Container Element - Bag
The subject “Car” is described by the predicate “equipment”.
<rdf:RDF xmlns:rdf="
xmlns:e="
<rdf:Description rdf:about="
<e:equipment>
<rdf:Bag>
<rdf:li rdf:resource="
<rdf:li rdf:resource="
<rdf:li rdf:resource="
</rdf:Bag>
</e:equipment>
</rdf:Description>
</rdf:RDF>
The different members of the Bag container
are listed.
The object is a container of type “Bag”
<x:xyz>
Defines predicate “xyz” in namespace “x”.
<rdf:Bag>
Defines a container of type “Bag”.
<rdf:li>
Defines members of the Bag container.
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28. Container Element - Sequence
“A Sequence or Seq (a resource having type rdf:Seq) represents a group of resources or literals, possibly including duplicate members, where the order of the members is significant.”
Example:
Describe a list of previous owners of the car in chronological order.
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29. Container Element - Sequence
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30. Container Element - Sequence
The subject “Car” is described by the predicate “preOwners”.
<rdf:RDF xmlns:rdf="
xmlns:p="
<rdf:Description rdf:about="
<p:preOwners>
<rdf:Seq>
<rdf:li rdf:resource="
<rdf:li rdf:resource="
<rdf:li rdf:resource="
</rdf:Seq>
</p:preOwners>
</rdf:Description>
</rdf:RDF>
The different members of the Sequence container are listed.
The object is a container of type “Sequence”.
<x:xyz>
Defines predicate “xyz” in namespace “x”.
<rdf:Seq>
Defines a container of type “Sequence”.
<rdf:li>
Defines members of Sequence container.
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31. Container Element - Alternative
“An Alternative or Alt (a resource having type rdf:Alt) represents a group of resources or literals that are alternatives (typically for a single value of a property).”
Example:
Describe a list of possible colors of the car.
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32. Container Element - Alternative
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33. Container Element - Alternative
The subject “Car” is described by the predicate “colors”.
<rdf:RDF xmlns:rdf="
xmlns:c="
<rdf:Description rdf:about="
<c:colors>
<rdf:Alt>
<rdf:li rdf:resource="
<rdf:li rdf:resource="
<rdf:li rdf:resource="
</rdf:Alt>
</c:colors>
</rdf:Description>
</rdf:RDF>
The different members of the Alternative container are listed.
The object is a container of type “Alternative”.
<x:xyz>
Defines predicate “xyz” in namespace “x”.
<rdf:Alt>
Defines a container of type “Alternative”.
<rdf:li>
Defines members of Alternative container.
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34. RDF Collections
A RDF Container can be used to define groups, but lacks the ability to “close” them. That means to define that "these are all the members of the container".
RDF Collections provide the ability to describe groups, that contain only the specified resources.
“An RDF collection is a group of things represented as a list structure in the RDF graph.”
Example:
All equipment features of a car.
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35. RDF Collection http://example.org/Car
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36. The predicate “equipment” is described by a Collection.
RDF Collection
The predicate “equipment” is described by a Collection.
<rdf:RDF xmlns:rdf="
xmlns:e="
<rdf:Description rdf:about="
<e:equipment rdf:parseType="Collection">
<rdf:Description rdf:about="
<rdf:Description rdf:about="
<rdf:Description rdf:about="
</e:equipment>
</rdf:Description>
</rdf:RDF>
<x:xyz rdf:parseType=“Collection”>
Defines that the predicate “xyz” is described by a collection.
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37. Validation Tool http://www.w3.org/RDF/Validator/
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38. Semantic Layer Web Cake
Web Engineering WT 2006/07 Chapter 4: Web Services
Semantic Layer Web Cake
A model for describing resources with properties and property values.
A format for specifying structured data in a machine-readable form
Unique identification
of resources
Semantic Web Layer Cake, Image source:
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© Gregor Engels University of Paderborn

39. How do I get all black Jaguars? RDF
RDF provides a model for describing resources with properties and property values.
@prefix ex: <
ex:Car1 ex:Brand ex:Jaguar
ex:Car1 ex:Colour “Black”
ex:Car2 ex:Brand ex:Jaguar
ex:Car2 ex:Colour “White”
ex:Car3 ex:Brand ex:VW
ex:Car3 ex:Colour “Black”
How do I get all
black Jaguars?
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40. SPARQL SPARQL Protocol and RDF Query Language
W3C Recommendation since 2008
SPARQL provides a standard for querying information, that is specified in RDF
SPARQL consists of three specifications
Query language
Query results XML format
Data access protocol
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41. Exemplary SPARQL Query
Web Engineering WT 2006/07 Chapter 4: Web Services
Exemplary SPARQL Query
“Return the models and prices for all cars of brand ‘Jaguar’ ” SPARQL Query: Exemplary Result:
Declares namespaces for abbreviated resources identifiers.
PREFIX ex: <
SELECT ?model ?price
WHERE
{ ?car ex:Brand ex:Jaguar .
?car ex:Model ?model .
?car ex:Price ?price . }
Identifies the variables to appear in the query results.
Provides the basic graph pattern to match against the data graph.
Model
Price
“XJ”
“79.750,00”
“XF”
“44.900,00”
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© Gregor Engels University of Paderborn

42. Basic Graph Patterns (BGP)
A SPARQL query contains a set of triple patterns called a basic graph pattern
Triple patterns are like RDF triples except that each of the subject, predicate and object may be a variable.
A basic graph pattern matches a subgraph of the RDF data when RDF terms from that subgraph may be substituted for the variables and the result is a RDF graph equivalent to the subgraph.
Variables are defined by “?varname” or “$varname”
WHERE
{ ?car ex:Brand ex:Jaguar .
?car ex:Model ?model .
?car ex:Price ?price . }
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43. Group Graph Patterns
“For a Group Graph Pattern, a set of graph patterns must all match”
In a SPARQL query string, a group graph pattern is delimited with braces: {...}
PREFIX ex: <
SELECT ?model ?price
WHERE
{ { ?car ex:Brand ex:Jaguar .
?car ex:Model ?model . }
?car ex:Price ?price . }
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44. Optional Pattern Matching
Basic graph patterns allow applications to make queries where the entire query pattern must match.
It is useful to be able to have queries that allow information to be added to the solution where the information is available, but do not reject the solution because some part of the query pattern does not match.
If the optional part does not match, it creates no bindings but does not eliminate the solution.
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45. Optional Pattern Matching
Web Engineering WT 2006/07 Chapter 4: Web Services
Optional Pattern Matching
Example:
Result
PREFIX ex: <
SELECT ?model ?price
WHERE
{ ?car ex:Brand ex:Jaguar .
?car ex:Model ?model .
OPTIONAL { ?car ex:Price ?price . } }
Model
Price
“XJ”
“79.750,00”
“XF”
“44.900,00”
“S-Type”
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© Gregor Engels University of Paderborn

46. Scope of Filters
“A constraint, expressed by the keyword FILTER, is a restriction on solutions over the whole group in which the filter appears.”
Result:
PREFIX ex: <
SELECT ?model ?price
WHERE
{ ?car ex:Brand ex:Jaguar .
?car ex:Model ?model .
?car ex:Price ?price .
FILTER (?price < ,00) }
Model
Price
“XF”
“44.900,00”
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47. Unary Operators (1/2) Operator Type(A) Result Type BOUND(A) variable
xsd:boolean
IsURI(A)
RDF term
isBLANK(A)
isLITERAL(A)
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48. Unary Operators (2/2) Operator Type(A) Result Type STR(A) literal
simple literal
URI / IRI
LANG(A)
DATATYPE(A)
typed literal
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49. Binary Operators (1/2) Operator Type(A) Type(B) Result Type A = B
numeric
simple literal
xsd:string
xsd:boolean
xsd:dateTime
A != B
A < B
A > B
A <= B
A >= B
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50. Binary Operators (2/2) Operator Type(A) Type(B) Result Type sameTERM
(A,B)
RDF term
xsd:boolean
langMATCHES(A,B)
simple literal
REGEX
Filter can be combined by “&&” or “||”
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51. Alternative Graph Patterns
“SPARQL provides a means of combining graph patterns so that one of several alternative graph patterns may match. If more than one of the alternatives matches, all the possible pattern solutions are found.”
Pattern alternatives are syntactically specified with the UNION keyword.
PREFIX ex: <
SELECT ?office
WHERE
{ ?x rdf:type ex:CarManufacturer .
{ ?x ex:Headquarter ?office . } UNION
{ ?x ex:Office ?office . } }
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52. Solution Sequences and Modifiers
“Query patterns generate an unordered collection of solutions. These solutions are then treated as a sequence (a solution sequence), initially in no specific order; any sequence modifiers are then applied to create another sequence.”
There are several use cases in which the results shall be presented in a defined order, e.g. alphabetical order
Shall duplicates be presented or deleted?
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53. Order By
“Following the ORDER BY clause is a sequence of order comparators, composed of an expression and an optional order modifier (either ASC() or DESC()). Each ordering comparator is either ascending (indicated by the ASC() modifier or by no modifier) or descending (indicated by the DESC() modifier).”
PREFIX ex: <
SELECT ?constructionYear ?price
WHERE { ?car ex:Brand ex:Jaguar .
?car ex:ConstructionYear ?constructionYear .
?car ex:Price ?price . }
ORDER BY DESC(?constructionYear) ?price .
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54. Some more Solution Sequence Modifiers
Web Engineering WT 2006/07 Chapter 4: Web Services
Some more Solution Sequence Modifiers
LIMIT
“The LIMIT clause puts an upper bound on the number of solutions returned. If the number of actual solutions is greater than the limit, then at most the limit number of solutions will be returned.”
OFFSET
“OFFSET causes the solutions generated to start after the specified number of solutions. An OFFSET of zero has no effect.”
SELECT DISTINCT
“The DISTINCT solution modifier eliminates duplicate solutions. Duplicates are eliminated before either limit or offset is applied.”
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© Gregor Engels University of Paderborn

55. Semantic Web Layer Cake
Web Engineering WT 2006/07 Chapter 4: Web Services
Semantic Web Layer Cake
A language for querying information specified in RDF.
A model for describing resources with properties and property values.
A format for specifying structured data in a machine-readable form
Unique identification
of resources
Semantic Web Layer Cake, Image source:
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© Gregor Engels University of Paderborn

56. Lessons Learned Now you should know ...
... the general idea of the Semantic Web and the differences to the World Wide Web.
... the underlying technologies of the Semantic Web.
... how resources can be identified and specified.
.. the importance of XML for expressing data in a machine-readable way.
... the concept of the RDF and the way it is expressed (e.g.: RDF/XML).
... how SPARQL can used to query data specified in RDF.
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57. References and Additional Material
Introduction to RDF
RDF Syntax Specification
RDF Validation Tool
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