Module 2b: Modeling Information Objects and Relationships

1
Module 2b Modeling Information Objects and
Relationships

• IMT530 Organization of Information Resources
• Winter, 2008
• Michael Crandall

2
Recap

• Information storage and retrieval systems (ISARs)
  are part of a larger knowledge system
• Within an ISAR, two inputs (user needs and
  entities) are combined to produce an answer for
  the users question
• To make that happen, both users queries and
  information entities need to be represented in
  some way

3
Module 2b Outline

• Models
• The entity-relationship model for database design
• Resource Description Framework for the web
• Syntax vs. semantics
• Ontologies and their place

4
What is a Model?

• A model represents a particular view of reality
  through a systematic set of rules
• As youve seen with vocabularies, a
  representation is only that, not reality
• In information systems, we are attempting to
  represent objects and their relationships
• This can become very complex, very quickly
• A way to manage this complexity is critical for
  success
• Models allow multiple systems to interact and
  share information more effectively
• Think of the earlier slide showing MSWebs search
  service- outside sources sharing the same model
  can provide much richer information to the system
  (and ultimately the users)

5
Sources of Models

• Database world
• Entity-relationship model
• Programming world
• Object oriented programming
• Information science world
• Functional Requirements for Bibliographic Records
• Dublin Core
• Web world
• Resource Description Framework
• Ontology Web Language

6
Database Modeling

• Chen developed concept of entities and
  relationships
• Entities are things which can be described
• Relationships are associations between entities
• These have attributes which are instantiated in
  values
• Allows description of complex spaces through
  diagrams showing how entities relate to other
  entities (tuples)
• Represented in tables within databases
• Essential in relational database modeling

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Example of E-R Model
From Chen, 1985
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How RDF Works

• RDF is based on the idea that
• Things being described (the Subject)
• Have properties (the Predicate),
• Which have values (the Object)
• And that resources can be described by making
  statements that specify those properties and
  values (triples)
• RDF models statements as nodes and arcs in a
  graph. In this notation, a statement is
  represented by
• a node for the subject
• a node for the object
• an arc for the predicate, directed from the
  subject node to the object node.

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How RDF Works

• This is done using URIs (Uniform Resource
  Identifiers) that can be created to refer to
  anything that needs to be referred to in a
  statement, including
• network-accessible things, such as an electronic
  document, an image, a service (e.g., "today's
  weather report for Los Angeles"), or a group of
  other resources.
• things that are not network-accessible, such as
  human beings, corporations, and bound books in a
  library.
• abstract concepts that do not physically exist,
  such as the concept of a "creator".

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An Example

• http//www.example.org/index.html has a creator
  whose value is John Smith
• could be represented by an RDF statement having
• a subject http//www.example.org/index.html
• a predicate http//purl.org/dc/elements/1.1/creato
  r
• and an object http//www.example.org/staffid/85740
  

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Example of RDF Model
Figure 1 An RDF Graph Describing Eric Miller
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RDF in XML

• lt?xml version"1.0"?gt
• ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
  df-syntax-ns" xmlnscontact"http//www.w3.org/20
  00/10/swap/pim/contact"gt
• ltcontactPerson rdfabout"http//www.w3.org/
  People/EM/contactme"gt
• ltcontactfullNamegtEric
  Millerlt/contactfullNamegt
• ltcontactmailbox rdfresource"mailtoem
  _at_w3.org"/gt
• ltcontactpersonalTitlegtDr.lt/contactpers
  onalTitlegt
• lt/contactPersongt
• lt/rdfRDFgt

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Syntax vs. Semantics

• Note that models are distinct from the language
  used to represent them
• An RDF model can be written in XML, but is
  independent of the language
• The reason XML becomes important is for machine
  to machine communication
• Allows recognition of structures and semantics in
  a common way, promoting interoperability at the
  syntax level
• Semantics are controlled by the model
• Different models may not communicate even if
  youre using XML
• So defining and standardizing your semantic model
  is critical for true interoperability

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Ontologies

• Semantic web is next step to embed semantics in
  syntax- but you need to model namespaces to do
  this
• Rich namespaces are being modeled through
  ontologies- an extension of classification theory
  that includes many more relationship types
• Qin and Paling on advantages of ontology
• Higher levels of conception of descriptive
  vocabulary
• Deeper semantics for class/subclass and
  cross-class relationships
• Ability to express such concepts and
  relationships in a description language
• Reusability and share-ability of the ontological
  constructs in heterogeneous systems
• OWL (Web Ontology Language) is current favorite
  tool (http//www.w3.org/TR/owl-features/)

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Ontology Example

• http//www.aiai.ed.ac.uk/project/enterprise/enterp
  rise/ontology.html

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Questions??

• And then a break.

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Exercise 2b

• Assemble your group
• Spend 45 minutes working through the examples in
  Exercise 2b
• Ask questions and talk!!!
• Be sure to hand in completed work at the end of
  class for credit!!!

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Example of Integration

• lt!--RDF Model 1--gt
• ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
  df-syntax-ns"
• xmlnseg"http//example.org/foovocab"
• xmlnsfoaf"http//xmlns.com/foaf/0.1/"gt
• ltfoafPerson rdfnodeID"p1"gt
• ltfoafnamegtAlicelt/foafnamegt
• ltfoafknows rdfnodeID"p2"/gt
• ltegacquaintance rdfnodeID"p2"/gt
• ltegarchNemesis rdfnodeID"p2"/gt
• lt/foafPersongt
• ltfoafPerson rdfnodeID"p2"gt
• ltfoafnamegtBoblt/foafnamegt
• ltegsecretlyStalking rdfnodeID"p1"/gt
• lt/foafPersongt
• lt/rdfRDFgt

• lt!--RDF Integrate Model 3--gt
• ltrdfRDF xmlnsrdf"http//www.w3.org/1999/02/22-r
  df-syntax-ns"
• xmlnseg"http//example.org/foovocab"
• xmlnsfoaf"http//xmlns.com/foaf/0.1/"gt
• ltfoafPerson rdfnodeID"p1"gt
• ltfoafnamegtAlicelt/foafnamegt
• ltfoafknows rdfnodeID"p2"/gt
• ltegacquaintance rdfnodeID"p2"/gt
• ltegarchNemesis rdfnodeID"p2"/gt
• lt/foafPersongt
• ltfoafPerson rdfnodeID"p2"gt
• ltfoafnamegtBoblt/foafnamegt

Contributed by Oknam Park
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Modeling Wrapup

• One model will not fit all needs
• More and more, integration of web models with
  database and programming models is becoming
  important
• Each will provide a different view of the world
  you are trying to manage
• Finding linkages for interoperability is the big
  challenge
• Well look next week at some current attempts in
  this area
• Think about how you would approach these problems
  and see how it fits what you read

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Next Week

• Well hear from a guest speaker about commercial
  use of ontologies
• Well dive into metadata schemas and schemes and
  the world of standards
• Remember to read next weeks assignments BEFORE
  class
• Have a great weekend!!