1. Logics for Data and Knowledge Representation
Resource Description Framework (RDF)
Feroz Farazi 1

2. RDF
Definitions
A language for representing Web resources and information about them in the form of metadata [RDF Primer]
A language to represent all kinds of things that can be identified on the Web [RDF Primer]
A domain independent data model for representing information on the Web [G. Antoniou and F.v. Harmelen, 2004]
A language with an underlying model designed to publish data on the Semantic Web [F. Giunchiglia et al., 2010]

3. RDF Keys Resource Property Statement
A thing or a class or an entity we want to talk about
For example, web pages, articles, authors, etc.
Property
metadata of the resources to be described
For example, creator, date of creation, publisher, etc.
Statement
A piece of information about a resource represented using a property and a value
For example, Tim Berners-Lee authored Weaving the Web. In other words, Weaving the Web has an author (or creator) whose value is Tim Berners-Lee.
A subject (Weaving the Web)–predicate (creator)–object (Tim Berners-Lee) triple

4. Statements In RDF, statements become machine comprehensible as
Triple elements are represented in a form of machine processable identifiers
They are encoded in a machine processable language
Identifiers
URL: Uniform Resource Locator
URI: Uniform Resource Identifier
URI includes
Things that can be located on the web (using URL), e.g., a home page of a person
Things that are not web accessible, e.g., a real world concept or entity
Language
RDF defines a specific XML language called RDF/XML

5. RDF Data Model A graph data model with directed edges
URIs to identify nodes (subject and object) and edges (predicate)
Objects can be literals: plain and typed
GeoNames has coverage of all countries
GeoNames was modified on
April 25, 2009

6. RDF Representations
The graph is a powerful tool for the understanding of the people
For the Semantic Web we need machines to understand and process
Simple statements are represented as triples in RDF/XML
RDF statements have similarity to
The entries in the data processing systems
The rows in the relational database tables
The assertions in logic languages
An RDF document
Contains an element enclosed in XML tag rdf:RDF
A set of descriptions can be defined within this element with the tag rdf:Description
Each description makes a set of statements about a resource, where
The resource can be defined newly with rdf:ID
It can refer to an existing resource with rdf:about

7. RDF Representations
Structured attributes (e.g., address) can be represented
Blank nodes or anonymous resources are used
Group of things (e.g., a conference participants) can be represented
RDF Containers can be used
Constructs are rdf:Bag, rdf:Seq, rdf:Alt
Container content are called members, which are listed using rdf:li
RDF Collections can be used
Can represent a close list overcoming the limitation of Containers
Constructs are rdf:List, rdf:first, rdf:rest, rdf:nil
Provenance of the statements (e.g., who, when) can be represented
RDF Reification is the means to represent statements about statements
Constructs are rdf:Stament, rdf:subject, rdf:predicate and rdf:object

8. XML Syntax for RDF RDF/XML: <?xml version=“1.0”?> <rdf:RDF
xmlns:rdf="
xmlns:rdfs="
xmlns:dc="
<rdf:Description rdf:about="
<rdfs:label>GeoNames</rdfs:label>
<dc:coverage rdf:resource="
<dc:modified>April 25, 2009</dc:modified>
</rdf:Description>
</rdf:RDF>

9. RDF Schema (RDFS)
A language for depicting the vocabulary of RDF developed to describe resources and relations between them [RDF Schema]
A language defined to provide mechanisms to add semantics to RDF resources [RDF Schema]
From the type system (classes and properties) perspective it has similarity to the object-oriented programming (OOP) paradigm
Differs from this paradigm in terms of defining classes and properties
In OOP, usually, classes are defined with respect to the properties an instance may have
In RDF Schema properties are defined with respect to the classes of the resources they can be attached to

10. Application: RDF vs Database
Query Engine
Database
Application
Query Engine
RDF Store
(merge)
Application
RDF Files
Unstructured formats (Web pages),
Structured formats (CSV, Excel and Databases)
Parser
Serializer
Converters and scrapers
Both applications have
A query engine
A storage
RDF applications also have
parser, serializer, converter and scraper
RDF merge functionality
Some example applications are calendar integration, map integration and annotation
[D. Allemang and J. Hendler, 2008]

11. RDF Inferencing In RDFS, semantics can be expressed through inferences
It allows type (rdf:type) propagation through rdfs:subClassOf
:Fausto_Giunchiglia rdf:type :Prfoessor
:Professor rdfs:subClassOf :Faculty
:Fausto_Giunchiglia rdf:type :Faculty (inferred)
It allows relationship propagation thgorugh rdfs:subPropertOf
:prfoessorshipAt rdfs:subProperytOf :affiliationWith
:Fausto Giunchiglia :professorshipAt :UniTN
:Fausto_Giunchiglia :affiliationWith :UniTN (inferred)
It allows type identification through rdfs:domain
:professorshipAt rdfs:domain :Person
:Fausto_Giunchiglia :professrshipAt :UniTn
:Fausto_Giunchiglia rdf:type :Person

12. RDF Inferencing It allows type identification through rdfs:range
:professorshipAt rdfs:range :Educational_Institution
:Fausto_Giunchiglia :professrshipAt :UniTn
:UniTn rdf:type :Educational_Institution (inferred)
Inferencing through rdfs:domain and rdfs:subClassOf
:Researcher rdfs:subClassOf :Scientist
:hIndex rdfs:domain :Researcher
:Fausto_Giunchiglia :hIndex 44
:Fausto_Giunchiglia rdf:type :Researcher (inferred)
:Fausto_Giunchiglia rdf:type :Scientist (inferred)
Inferencing through rdfs:range and rdfs:subClassOf
:Educational_Institution rdfs:subClassOf :Organization
:professorshipAt rdfs:range : Educational_Institution
:Fausto_Giunchiglia :professorshipAt :UniTn
:UniTn rdf:type :Organization (inferred)

13. RDF Modeling Modeling (logical) Set Intersection in RDF
Can we represent that “If an entity e is in X, it is also in both Y and Z”?
No explicit modeling construct is provided to do that but Can be modeled as:
X rdfs:subClassOf Y
X rdfs:subClassOf Z
e rdf:type X
e rdf:type Y (inferred)
e rdf:type Z (inferred)
Modeling (logical) Set Union in RDF
Can we represent “Any entity e that belongs either to Y or Z also belongs to X”?
Y rdfs:subClassOf X
Z rdfs:subClassOf X
e rdf:type Y or
e rdf:type Z
e rdf:type X (inferred)

14. References RDF Primer (2004). W3C Recommendation.
RDF Schema (2004). W3C Recommendation.
G. Antoniou & F. van Harmelen (2004). A Semantic Web Primer (Cooperative Information Systems). MIT Press, Cambridge MA, USA.
F. Giunchiglia, F. Farazi, L. Tanca, and R. D. Virgilio. The semantic web languages. In Semantic Web Information management, a model based perspective. Roberto de Virgilio, Fausto Giunchiglia, Letizia Tanca (Eds.), Springer, 2009.
D. Allemang and J. Hendler. Semantic web for the working ontologist: modeling in RDF, RDFS and OWL. Morgan Kaufmann Elsevier, Amsterdam, NL, 2008.