The document provides an overview of the Semantic Web including definitions of key concepts like RDF, RDFS, OWL, and applications. It describes the Semantic Web as extending the current web to give data well-defined meaning enabling computers and people to better cooperate. The layers of the Semantic Web are outlined including XML, RDF, RDFS, OWL, and how each builds on the previous. Examples of RDF graphs and syntax are given. Semantic Web applications like Swoogle, DBpedia, and Flickr are also mentioned.

1. Semantic Web

2. Overview
 What is Semantic Web
 Semantic Web Vision
 Semantic Web Layers
 RDF, RDFS, OWL
 Tools
 GATE
 Applications

3. What is Semantic Web?
 Semantic means that the meaning of data
can be discovered by computers
 "The Semantic Web is an extension of the
current web in which information is given
well-defined meaning, better enabling
computers and people to work in
cooperation." - Tim Berners-Lee

4. Definition
 The Semantic Web is a project to create a
universal medium for information exchange by
putting documents with computer-processable
meaning (semantic) on the World Wide Web
 The Semantic Web extends the Web through the
use of standards, markup languages and related
processing tools

5. The aims of Semantic Web
 Indexing and retrieving information
 Annotation
 The Web as a interoperable database
 Machine retrieval of data
 Web based services
 Discovery of services
 Intelligent software agents

6. Semantic Web Vision
 Oriented toward machine-readable
resources rather than human-readable
 Requires resources to be described so
that machines know what they mean
 Description in terms of metadata
 Use of logic interpretation for inference

7. Semantic Web Layers

8. Semantic Web Layers
 XML (Extensible Markup Language)- The
language framework that is used to define
nearly all new languages that are used to
interchange data over the Web
 XML Schema -A language used to define
the structure of specific XML language

9. Semantic Web Layers
 RDF (Resource Description Framework)-
a language used to describe all sort of
information and meta data
 RDF Schema-A framework that provides a
means to specify basic vocabularies for
specific RDF application language to use

10. Semantic Web Layers
 Ontology- defines vocabularies and
establish the usage of words and terms in
context of specific vocabulary
 Logic and Proof –is used to establish the
consistency and correctness of data sets
and to infer conclusion that aren’t explicitly
stated

11. Semantic Web agents
 Metadata will be used to identify and
extract information from Web sources.
 Ontologies will be used to assist in Web
searches, to interpret retrieved
information, and to communicate with
other agents.
 Logic will be used for processing retrieved
information and for drawing conclusions.

12. RDF

13. RDF
• “Resource Description Framework”
• RDF is a data model
• Originally for describing metadata for web pages
• Structured information
• Universal, machine-readable data exchange model
• Syntax uses XML for serialization
• Statements can be modeled with
• Resources: an element, a URI, a literal
• Properties: directed relation between two resources
• Statements: triples of two resources linked by property

14. RDF
• Generally triple can be viewed as a graph
• both “ object: and “ subject” are the graph nodes
• “properties are the edges
• XML syntax is only the tools for practical usage instead of graph
• Components
• URIs – for referencing resources
• Literals – data values
• Empty nodes (blank nodes) – talking about something which doesn’t
have a name

15. RDF Example
• Subject: URIs and empty nodes
• Predicate: URIs ( also called properties)
• Object: URIs and empty nodes and literals

16. XML syntax for RDF Example

17. RDF Example

18. RDF XML Code Example
1. <?xml version="1.0"?>
2. <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
3. xmlns:dc="http://purl.org/dc/elements/1.1/"
4. xmlns:exterms="http://www.example.org/terms/">
5. <rdf:Description rdf:about="http://www.example.org/index.html">
6. <exterms:creation-date>August 16, 1999</exterms:creation-date>
7. <dc:language>en</dc:language>
8. <dc:creator rdf:resource="http://www.example.org/staffid/85740"/>
9. </rdf:Description>
10. </rdf:RDF>

19. A simple example
 “The book has the title War and Peace”
 Graphical RDF Statement
has the title War and
The book
The book Peace
 RDF in a XML document
<?xml version="1.0"?>
<rdf:RDF
xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#"
xmlns:dc="http://purl.org/dc/element/1.1">
<rdf:Description rdf:about="http://amazon.com/books">
<dc:title> War and Peace</dc:title>
</rdf:Description>
</rdf:RDF>

20. Ontology
 We can express ontology as:
Ontology =<taxonomy, inference rules>
And we can express a taxonomy as:
Taxonomy <{classes}, {relations}>
 Ontology Languages (RDFS, OWL) has formal
foundations that allow us to infer additional (implicit)
statements

21. RDF Schema
 Intended to structure RDF resources
 RDFS
 Set theory – rdfs:Class
 Relation – rdf:Property, rdfs:domain, rdfs:range
 Hierarchy – rdfs:subClassOf, rdfs:subPropertyOf
 Built-in Datatype – xsd:string, xsd:dataTime

22. RDF & RDFS
 RDF is graphical formalism ( + XML syntax + semantics)
 for representing metadata
 for describing the semantics of information in a
machine- accessible way
 RDFS extends RDF with “schema vocabulary”, e.g.:
 Class, Property
 type, subClassOf, subPropertyOf
 range, domain

23. Limitations of RDF/RDFS
 No standard for expressing primitive data types such as
integer, etc. All data types in RDF/RDFS are treated as
strings.
 No standard for expressing relations of properties
(unique, transitive, inverse etc.)
 No standard for expressing whether enumerations are
closed.
 No standard to express equivalence, disjointedness etc.
among properties

24. OIL and DAML
 RDFRDFS define a framework, however they have
limitations. There is a need for new semantic web
languages with following requirements
 They should be compatible with (XML, RDF/RDFS)
 They should have enough expressive power to fill in the gaps in
RDFS
 They should provide automated reasoning support
 Ontology Inference Layer (OIL) and DARPA Agent Markup
Language (DAML) are two important efforts developed to
fulfill these requirements.
 Their combined efforts formed DAML+OIL declarative
semantic language.

25. OIL and DAML
 DAML+OIL is built on top of RDFS.
 It uses RDFS syntax.
 It has richer ways to express primitive data types.
 DAML+OIL allows other relationships (inverse and
transitivity) to be directly expressed.
 DAML+OIL provides well defined semantics, This
provides followings:
 Meaning of DAML+OIL statements can be formally specified.
 Machine understanding and automated reasoning can be
supported.
 More expressive power can be provided.

26. Example
Example: T. Rex is not herbivore and not a currently living
species.
 This statement can be expressed in DAML+OIL, but not in
RDF/RDFS since RDF/RDFS cannot express disjointedness.
 DAML+OIL provides automated reasoning by providing such
expressive power.
 For instance, a software agent can find out the “list of all the carnivores
that won’t be any threat today” by processing the DAML+OIL data
representation of the example above.
 RDF/RDFS does not express “is not” relationships and exclusions.

27. OWL

28. Web Ontology Language = OWL
 OWL is an extra layer, a bit like RDFS
 own namespace, own terms
 it relies on RDF Schemas
 It is a separate recommendation
 actually… there is a 2004 version of OWL
(“OWL 1”)
 and there is an update (“OWL 2”) published in
2009

29. OWL- Web Ontology Language
 OWL is a vocabulary extension of the RDF and is
derived from the DAML+OIL Web Ontology Language.
 OWL
 Description Logic
 Class, Thing, Nothing
 DatatypeProperty, ObjectProperty, AnnotationProperty,…
 Class
 oneOf, disjointWith, unionOf, complementOf, intersectionOf …
 Restriction, onProperty, cardinality, hasValue…
 Property
 inverseOf , TransitiveProperty , SymmetricProperty
 FunctionalProperty, InverseFunctionalProperty
 Equality– equivalentClass , sameAs , differentFrom…
 Ontology annotation – Ontology, imports, versionInfo

30. Term equivalences
 For classes:
 owl:equivalentClass: two classes have the
same individuals
 owl:disjointWith: no individuals in common
 For properties:
 owl:equivalentProperty
 remember the a:author vs. f:auteur?
 owl:propertyDisjointWith

31. Term equivalences
 For individuals:
 owl:sameAs: two URIs refer to the same
concept (“individual”)
 owl:differentFrom: negation of owl:sameAs

32. Example
owl:equivalentProperty
a:author f:auteur
owl:equivalentClass
a:Novel f:Roman

33. Property characterization
 In OWL, one can characterize the
behavior of properties (symmetric,
transitive, functional, reflexive, inverse
functional…)
 One property can be defined as the
“inverse” of another

34. What this means is…
 If the following holds in our triples:
:email rdf:type owl:InverseFunctionalProperty.
<A> :email "mailto:a@b.c".
<B> :email "mailto:a@b.c".

35. What this means is…
 If the following holds in our triples:
:email rdf:type owl:InverseFunctionalProperty.
<A> :email "mailto:a@b.c".
<B> :email "mailto:a@b.c".
then, processed through OWL, the following
holds, too:
<A> owl:sameAs <B>.

36. Keys
“if two persons have the same emails and the same
homepages then they are identical”
 Identification is based on the identical
values of two properties
 The rule applies to persons only

37. Previous rule in OWL
:Person rdf:type owl:Class;
owl:hasKey (:email :homepage) .

38. What it means is…
If:
<A> rdf:type :Person ;
:email "mailto:a@b.c";
:homepage "http://www.ex.org".
<B> rdf:type :Person ;
:email "mailto:a@b.c";
:homepage "http://www.ex.org".
then, processed through OWL, the following holds,
too:
<A> owl:sameAs <B>.

39. Classes in OWL
 In RDFS, you can subclass existing
classes… that’s all
 In OWL, you can construct classes from
existing ones:
 enumerate its content
 through intersection, union, complement
 etc

40. Enumerate class content
:Currency
rdf:type owl:Class;
owl:oneOf (:€ :£ :$).
 I.e., the class consists of exactly of those
individuals and nothing else

41. Union of classes
:Novel rdf:type owl:Class.
:Short_Story rdf:type owl:Class.
:Poetry rdf:type owl:Class.
:Literature rdf:type owl:Class;
owl:unionOf (:Novel :Short_Story :Poetry).
 Other possibilities: owl:complementOf,
owl:intersectionOf, …

42. For example…
If:
:Novel rdf:type owl:Class.
:Short_Story rdf:type owl:Class.
:Poetry rdf:type owl:Class.
:Literature rdf:type owl:Class;
owl:unionOf (:Novel :Short_Story :Poetry).
<myWork> rdf:type :Novel .
then the following holds, too:
<myWork> rdf:type :Literature .

43. What we have so far…
 The OWL features listed so far are already
fairly powerful
 E.g., various databases can be linked via
owl:sameAs, functional or inverse
functional properties, etc.
 Many inferred relationship can be found
using a traditional rule engine

44. The most used Semantic Web
Tools
 RDF Gateway- it runs both a Web
application server and database design to
handle RDF content
 Jena -Java API for RDF
 Smore: Semantic Markup, Ontology and
RDF Editor
 Drive - a C# API. It parses and validate
RDF documents.

45. General Architecture for Text
Engineering (GATE)

46. What is GATE?
An architecture
A macro-level organisational picture for LE software systems.
A framework
For programmers, GATE is an object-oriented class library that
implements the architecture.
A development environment
For language engineers, computational linguists et al, GATE is a
graphical development environment bundled with a set of tools for doing
e.g. Information Extraction.
Some free components... ...and wrappers for other
people's components
Tools for: evaluation; visualise/edit; persistence; IR; IE; dialogue;
ontologies; etc.
46(21)

47. Where did GATE come from?
A number of researchers realised in the early- mid-1990s (e.g. in
TIPSTER):
• Increasing trend towards multi-site collaborative projects
• Role of engineering in scalable, reusable, and portable HLT solutions
• Support for large data, in multiple media, languages, formats, and
locations
• Lower the cost of creation of new language processing components
• Promote quantitative evaluation metrics via tools and a level playing field
History:
• 1996 – 2002: GATE version 1, proof of concept
• March 2002: version 2, rewritten in Java, component based, more users
• Fall 2003: new development cycle
47(21)

48. Applications
 Swoogle
 DBpedia
 Flickr
 PhotoStuff

49. Swoogle
• Swoogle is a crawler based indexing and retrieval
system for Semantic Web
• Swoogle crawls and discovers documents written in
RDF,OWL
• Swoogle classifies a Semantic Web
Document(SWD) as –
• Semantic Web Ontology (SWO) – Defines new
terms
• Semantic Web Databases (SWDB) – Makes
assertions about individuals

50. Reference & Resources
 http://www.w3.org/TR/rdf-primer/
 http://www.w3.org/DesignIssues/Semantic.html
 http://www.w3.org/TR/rdf-syntax-grammar/
 http://www.authorstream.com/Presentation/sneha.ch
 http://www.w3.org/TR/owl-semantics/