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The RDF meta model: a closer look


RDF provides three types of collection: rdf:Bag , rdf:Seq and rdf:Alt ... ELEMENT Value (#CDATA) XML Instance Resource id=' ... – PowerPoint PPT presentation

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Title: The RDF meta model: a closer look

The RDF meta model a closer look
  • Basic ideas of the RDF
  • Resource instance descriptions in the RDF format
  • Application-specific RDF schemas
  • Limitations of XML compared w/ RDF
  • The Dublin Core Standard
  • Metadata, ontology and information registry

Basic Ideas
  • Its all about machine-understandability and
  • resource discovery in building and maintaining
    search engines
  • cataloging for certain Web sites or a digital
  • sophisticated communication between intelligent
    software agents
  • Standardization at two levels
  • instance level all resource instances can be
    described in a uniformed format
  • schema level class, attribute and relationship
    definitions also in a uniformed format.
  • Conventional meta models only enforce the
    standardized format in the schema level, e.g.
    O.O., ER or other semantic models.

Resource instance descriptions
  • The RDF meta model contains the following three
    basic concepts
  • A resource can be anything describable using RDF.
    E.g., an entire web page, a whole collection of
    web pages, a web site. Even an object in the
    physical world such as a book.
  • A property is a specific aspect of a resource.
    It can be a characteristic that belongs to a
    resource, or a relationship that links one
    resource with another.
  • A statement is a piece of description about a
    particular resource in the RDF format.
  • All RDF keywords for the instance-level
    description start w/ rdf

Resource instance descriptions (contd)
  • A statement about a resource instance has
  • the resources identifier
  • one of the resources property (defined in an RDF
  • the value for that property (can be either a
    literal, or a resource)
  • ltrdfRDF xmlnswchttp//
  • ltrdfDescription abouthttp//
    EALTH/cancer/12/06/ colon.cancer.ap/index.htmlgt
  • ltwcTitlegtCigarette smoking linked to colorectal
    cancer lt/wcTitlegt
  • lt/rdfDescriptiongt
  • lt/rdfRDFgt

Resource instance descriptions (contd)
  • A property can be a collection of elements
  • RDF provides three types of collection
    ltrdfBaggt, ltrdfSeqgt and ltrdfAltgt
  • Collection specification at the instance rather
    than the schema level
  • ltrdfRDF
  • xmlnswchttp//
  • ltrdfDescription abouthttp//
    EALTH/cancer/12/06/ colon.cancer.ap/index.html
  • ltwcTitlegt
  • ltrdfAltgt
  • ltrdfli xmllangengtCigarette smoking …
  • ltrdfli xmllangitgt……lt/rdfligt
  • lt/rdfAltgt
  • lt/wcTitlegt
  • lt/rdfDescriptiongt
  • lt/rdfRDFgt

Resource Schema Specification
  • A schema in RDF is comparable to that in the O.O.
    model (a set of class definitions) or the ER
    model (a set of entity specifications)
  • User can define classes as well as an inheritance
  • Attributes of classes are separately defined as
    properties a major difference from
    conventional modeling methods.
  • All RDF keywords for the schema-level description
    start w/ rdfs

Resource Schema Specification Classes
  • A class definition in RDF is more like a class
    declaration in O.O. languages.
  • Keywords ltrdfsClassgt, ltrdfssubClassOfgt.
  • An example
  • ltrdfRDFgt
  • ltrdfsClass rdfIDMedicalDocumentsgt
  • ltrdfscommentgtThe set of all medical related
    documents. lt/rdfcommentgt
  • ltrdfssubClassOf rdfresourcehttp//www.w3.o
  • 01/rdf-schemaResource/gt
  • lt/rdfsClassgt
  • ltrdfsClass rdfIDPatientRecordsgt
  • ltrdfscommentgtThe set of patients records.
  • ltrdfssubClassOf rdfresourceMedicalDocumen
  • lt/rdfsClassgt
  • lt/rdfRDFgt

Resource Schema Specification Properties
  • Unlike conventional modeling methods where
    attributes are subordinates of classes, the
    Property concept in RDF is at the same level
    with the Class concept.
  • Properties are linked w/ classes via the domain
  • Benefit more flexibility and extensibility.
  • An example
  • … ltrdfsProperty rdfIDpatientIDgt ltrdfsdomai
    n rdfresourcePatientRecords/gt ltrdfsrange
    rdfresourcePatientIDClass/gt lt/rdfsPropertygt

Comparable to class PatientRecords
MedicalDocument PatientIDClass patientID
Limitations of XML compared w/ RDF
  • XML provides a standardized syntax for
    interoperability purpose, not on the semantics.
  • an XML parser can be reused anywhere
  • the XML parser cannot understand the semantics
    behind the syntax
  • for two parties to communicate, they have to
    agree upon certain semantic aspects of the

ltabc cd…gt … lt/abcgt
XML Parser (encoder)
XML Parser (decoder)
Limitations of XML (contd)
  • No fixed XML syntax to describe one fact
  • DTD 1
  • lt!ELEMENT Resource (property)gt
  • lt!ATTLIST Resource id (CDATA)gt
  • lt!ELEMENT property (Value)gt
  • lt!ATTLIST property name (CDATA)gt
  • lt!ELEMENT Value (CDATA)gt
  • XML Instance
  • ltResource idhttp//…/gt ltproperty
    nameTitlegt ltValuegtCigarette …
    lt/Valuegt lt/propertygt lt/Resourcegt
  • DTD 2
  • lt!ELEMENT property (Resource, Value)gt
  • lt!ATTLIST property name (CDATA)gt
  • lt!ELEMENT Resource (CDATA)gt
  • lt!ELEMENT Value (CDATA)gt
  • XML Instance
  • ltproperty nameTitlegt ltResourcegthttp//www.cnn.c
    om/…lt/Resourcegt ltValuegtCigarette … lt/Valuegt
  • lt/propertygt

The Dublin Core Standard
  • The Dublin Core Metadata Intiative
  • A standardized conceptual schema for describing
    web resources
  • Dublin Core Elements (attributes of a web
  • 15 pre-defined elements Title, Creator, Subject,
    Description, Publisher, Contributor, Date, Type,
    Format, Identifier, Source, Language, Relation,
    Coverage, Rights.
  • Dublin Core also defines a set of keywords
    associated with each element, called Dublin Core
    Qualifiers, to make the element instances more
  • E.g. a Date element may be further refined as
    Created Date, Valid Date, Available Date,
    Issued Date or Modified Date. The encoding
    scheme can be DCMI period or W3C-DTF.
  • The Dublin Core standard can be specified as an
    RDF Schema

Metadata, Ontology and Information Registry
  • Ontology
  • concept (class) graph about real world objects
  • Metadata
  • conceptually, people are committed to this de
    facto definition - structured data about data
  • practically, metadata is used to denote both
    data about data and data about real world
    objects (the ontology)
  • Information Registry
  • to free ourselves from the ambiguity of
    metadata, we can use information registry to
    denote structured data about data.
  • Both the ontology and the information registry
    can be represented in the RDF format

Ontology and Information Registry (contd)
Dublin Core Schema
Extended Schema
All specified in the RDF format
Resource Schema
Information Registry
described by
Information Resources
described by
Real World Objects
Current Tasks
  • Make a decision about which medical ontology to
    use. See if it is already specified in the RDF
  • Design the information registrys structure make
    extensions to existing schemas such as Dublin
  • Based on the medical ontology and the registry
  • design an algorithm for automatic resource
  • design an ontology-enhanced algorithm for content

  • RDF
  • a uniform format for resource instance as well as
    schema description
  • Dublin Core
  • a conceptual schema about web resources
  • Ontology
  • data about real world objects classes,
    inheritance, attribute, relationship
  • Information Registry
  • data about data various aspects of on-line
  • Information Resource Schema
  • schema for the information registry
  • All three (the ontology, the registry and the
    schema) will be specified in the RDF format