Why do we need an “Object Oriented Model” ?

1. Why do we need an “Object Oriented Model” ? Martin Doerr Institute of Computer Science Foundation for Research and Technology - Hellas Heraklion - Crete Atlanta, August 31, 2000

2. 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

3. 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

4. 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!

5. Extending the Relational Model:Specialization (refinement analysis) Relational form: Museum Artefact Holy Bread Basket type museum number TA 153 collection Byzantine silver material O-O Schema declaration (Classes): O-O Schema usage (Instances): Museum Artefact Holy Bread Basket museum number museum number TA 153 collection collection Byzantine silver material material Ecclesiastical item belongs to church belongs to church St. George of Andranopole Holy Bread Basket container TA 153’container container lid lid TA 153’lid

6. More Advanced Features:Multiple Inheritance (multiple higher terms) Single Inheritance form: Multiple Inheritance form: Museum Artefact Museum Artefact museum number museum number collection collection material material Ecclesiastical item Ecclesiastical item Canister Canister container container belongs to church belongs to church lid lid Holy Bread Basket Holy Bread Basket container lid Unique identity of properties ! Repetition of properties !

7. Problem of Global Searches:Identity of property Artefact Action Holy Bread Basket TA 153 Commemoration of Drakos Holy Bread Basket Offered Object Commemoration belongs to belongs to container TA 153’container date 1667 AD lid TA 153’lid place Adrianopole Drakos notion of action hidden ! donator Drakos subject acceptor St. George Church commemorating notion of action explicit Holy Bread Basket TA 153 Drakos’offer Holy Bread Basket Offered Object belongs to Offer belongs to date 1667 AD container TA 153’container Adrianopole place Drakos lid TA 153’lid subject St. George Church acceptor Drakos’offer offer normalized form

8. 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 ?

9. F5630288D67 3515020669 Karlsruhe, Germany Heraklion, Greece Martin Doerr Martin Dörr * E21 Person E72 Actor Appellation E45 Address E72 Actor Appellation E45 Address E72 Actor Appellation E72 Actor Appellation Object-orientated Semantic Models:Separating Identity From Description real world equivalents persistent identifiers fully qualified entities is identified by is identified by is identified by is identified by has contact point has contact point

10. Martin Doerr * Researcher Farmer Patient Research Field Illness Type Crop Type E72 Actor Appellation Knowledge Representation Paradontosis Olives Object-orientated Semantic Models: Multiple Instantiation is identified by suffers from is interested in cultivates Not three records, but one “dynamic record”, aggregate of applicable properties !

11. 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

12. 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

13. 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 !