Logics for Data and Knowledge Representation

1
Logics for Data and Knowledge Representation

• Resource Description Framework (RDF)

Feroz Farazi
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
• 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 rdfRDF
• A set of descriptions can be defined within this
  element with the tag rdfDescription
• Each description makes a set of statements about
  a resource, where
• The resource can be defined newly with rdfID
• It can refer to an existing resource with
  rdfabout

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 rdfBag, rdfSeq, rdfAlt
• Container content are called members, which are
  listed using rdfli
• RDF Collections can be used
• Can represent a close list overcoming the
  limitation of Containers
• Constructs are rdfList, rdffirst, rdfrest,
  rdfnil
• Provenance of the statements (e.g., who, when)
  can be represented
• RDF Reification is the means to represent
  statements about statements
• Constructs are rdfStament, rdfsubject,
  rdfpredicate and rdfobject

8
XML Syntax for RDF

• RDF/XML
• lt?xml version1.0?gt
• ltrdfRDF
• xmlnsrdf"http//www.w3.org/1999/02/22-rdf-synt
  ax-ns"
• xmlnsrdfs"http//www.w3.org/2000/01/rdf-schema
  "
• xmlnsdc"http//purl.org/dc/terms"gt
• ltrdfDescription rdfabout"http//www.geona
  mes.org"gt
• ltrdfslabelgtGeoNameslt/rdfslabelgt
• ltdccoverage rdfresource"http//www.geo
  names.org/countries"/gt
• ltdcmodifiedgtApril 25,
  2009lt/dcmodifiedgt
• lt/rdfDescriptiongt
• lt/rdfRDFgt

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

• 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 (rdftype) propagation through
  rdfssubClassOf
• Fausto_Giunchiglia rdftype Prfoessor
• Professor rdfssubClassOf Faculty
• Fausto_Giunchiglia rdftype Faculty (inferred)
• It allows relationship propagation thgorugh
  rdfssubPropertOf
• prfoessorshipAt rdfssubProperytOf affiliationWi
  th
• Fausto Giunchiglia professorshipAt UniTN
• Fausto_Giunchiglia affiliationWith UniTN
  (inferred)
• It allows type identification through
  rdfsdomain
• professorshipAt rdfsdomain Person
• Fausto_Giunchiglia professrshipAt UniTn
• Fausto_Giunchiglia rdftype Person

12
RDF Inferencing

• It allows type identification through rdfsrange
• professorshipAt rdfsrange Educational_Instituti
  on
• Fausto_Giunchiglia professrshipAt UniTn
• UniTn rdftype Educational_Institution
  (inferred)
• Inferencing through rdfsdomain and
  rdfssubClassOf
• Researcher rdfssubClassOf Scientist
• hIndex rdfsdomain Researcher
• Fausto_Giunchiglia hIndex 44
• Fausto_Giunchiglia rdftype Researcher
  (inferred)
• Fausto_Giunchiglia rdftype Scientist
  (inferred)
• Inferencing through rdfsrange and
  rdfssubClassOf
• Educational_Institution rdfssubClassOf Organiza
  tion
• professorshipAt rdfsrange Educational_Institut
  ion
• Fausto_Giunchiglia professorshipAt UniTn
• UniTn rdftype Educational_Institution
  (inferred)
• UniTn rdftype 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 rdfssubClassOf Y
• X rdfssubClassOf Z
• e rdftype X
• e rdftype Y (inferred)
• e rdftype 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?
• No explicit modeling construct is provided to do
  that but Can be modeled as
• Y rdfssubClassOf X
• Z rdfssubClassOf X
• e rdftype Y or
• e rdftype Z
• e rdftype 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.