ics – forth, august 31, 2000 why do we need an “object oriented model” ? martin doerr atlanta,...
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ICS – FORTH, August 31, 2000
Why do we need an “Object Oriented Model” ?
Martin Doerr
Atlanta, August 31, 2000
Foundation for Research and Technology - HellasInstitute of Computer Science
Heraklion - Crete
ICS – FORTH, August 31, 2000
History of object-oriented Databases
Successor of relational model (RDBMS) To handle
very complex data evolve gracefully provide high performance
Following o-o languages First defined `89
(The Object - Oriented Database System Manifesto)
Now in various forms and implementations
ICS – FORTH, August 31, 2000
Relevance of the O-O Paradigm
More complex to comprehend, but closer to human conceptualization Concept hierarchies Distinction of individuals and roles Making real world equivalents explicit Separation of identity and description
Allows for creating “knowledge bases” and information integration systems So-called semantic models, formal ontologies Global models comprising multiple data structures
ICS – FORTH, August 31, 2000
The Relational Model
Relation (table) : set of tuples (a1, a2, ..,an) fixed number of columns primitive typing of columns named relation, named columns
Relational databases : aggregation of tables data units/ records are identified by contents ! All fill-in forms follow same paradigm!
ICS – FORTH, August 31, 2000
Extending the Relational Model:
Specialization (refinement analysis)
Relational form:
O-O Schema usage (Instances):
Museum Artefact
type
museum number
material
TA 153
silver
Byzantinecollection
Holy Bread Basket
Museum Artefact
museum number
material
collection
Ecclesiastical item
belongs to church
Holy Bread Basket
container
lid
O-O Schema declaration (Classes):
Holy Bread Basket
museum number
material
TA 153
silver
Byzantinecollection
belongs to church
container
lid
St. George of Andranopole
TA 153’container
TA 153’lid
ICS – FORTH, August 31, 2000
More Advanced Features:Multiple Inheritance (multiple higher
terms)
belongs to church
Ecclesiastical item
Holy Bread Basket
container
lid
Museum Artefact
museum number
material
collection
Single Inheritance form:
Museum Artefact
museum number
material
collection
Multiple Inheritance form:
Canister
container
lid belongs to church
Ecclesiastical item Canister
container
lid
Holy Bread Basket
Repetition of properties ! Unique identity of properties !
ICS – FORTH, August 31, 2000
Problem of Global Searches:
Identity of property
Holy Bread Basket TA 153
belongs to
container
lid
donator
acceptor
Holy Bread Basket Offered Object
TA 153’container
TA 153’lid
Drakos
St. George Church
Artefact
Commemoration of Drakos
belongs to
date
place
subject
commemorating
Commemoration
1667 AD
Adrianopole
Drakos
Action
Holy Bread Basket TA 153
belongs to
container
lid
offer
Holy Bread Basket Offered Object
TA 153’container
TA 153’lid
Drakos’offer
Drakos’offer
belongs todate
subjectacceptor
Offer1667 AD
DrakosSt. George Church
Adrianopoleplace
notion of action hidden !
normalized form
notion of action explicit
ICS – FORTH, August 31, 2000
Insufficient Identity in Flat Records:
Two Different Persons!
Table Person
First name : Martin
Last name : Dörr
Passport Nr.: F5630288D67
City : Karlsruhe
Country : Germany
Table Person
First name : Martin
Last name : Doerr
Passport Nr.: 3515020669
City : Heraklion
Country : Greece
?
? Who am I ?
ICS – FORTH, August 31, 2000
Object-orientated Semantic Models:
Separating Identity From Description
E21 Person
*E72 Actor Appellation
Martin Dörris identified by
E72 Actor Appellation
Martin Doerris identified by
E72 Actor Appellation
F5630288D67is identified by
E72 Actor Appellation
3515020669is identified by
E45 Address
Karlsruhe, Germanyhas contact point
E45 Address
Heraklion, Greecehas contact point
real worldequivalents
persistent identifiers fully qualified entities
ICS – FORTH, August 31, 2000
Object-orientated Semantic Models: Multiple Instantiation
Researcher
*
is identified by is interested in
FarmerPatient
suffers from
cultivates
Research FieldKnowledge Representation
Illness Type Paradontosis
Crop Type Olives
E72 Actor Appellation
Martin Doerr
Not three records,but one “dynamic record”,aggregate of applicable properties !
ICS – FORTH, August 31, 2000
Requirements for Cultural Repositories
Cultural repositories need an o-o “global schema” As intermediate data format (“where data come together”) As reasoning component – to settle differences As adequate expression of the domain knowledge
Object-oriented semantic models are: Adequate State-of-the-art core components of repositories Standard (e.G. RDFS) Can be implemented on conventional platforms
ICS – FORTH, August 31, 2000
Requirements for Cultural Repositories
(Apologies for the computer jargon)
Object-oriented core features needed: object identity
value independent, perpetual, types and classes
user defined, meaning bound, extensible class or type hierarchy
multiple levels of abstraction inheritance of properties
explicit representation of properties extensibility
new subclasses, properties on existing body of data keeping up-to-date with an open world
ICS – FORTH, August 31, 2000
Conclusions
Object-oriented semantic models (domain ontologies) are adequate to create cultural repositories
They must be product of interdisciplinary work, a valid expression of expert knowledge!
The CIDOC Conceptual Reference Model is such a model !