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

ICS – FORTH, August 31, 2000 History of object-oriented Databases p Successor of relational model (RDBMS) p To handle u very complex data u evolve gracefully u provide high performance p Following o-o languages p First defined `89 (The Object - Oriented Database System Manifesto) p Now in various forms and implementations

ICS – FORTH, August 31, 2000 Relevance of the O-O Paradigm p More complex to comprehend, but closer to human conceptualization u Concept hierarchies u Distinction of individuals and roles u Making real world equivalents explicit u Separation of identity and description p Allows for creating “knowledge bases” and information integration systems u So-called semantic models, formal ontologies u Global models comprising multiple data structures

ICS – FORTH, August 31, 2000 The Relational Model p Relation (table) : u set of tuples (a1, a2,..,an) u fixed number of columns u primitive typing of columns u named relation, named columns p Relational databases : u aggregation of tables u data units/ records are identified by contents ! u 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 belongs to date subject acceptor Offer 1667 AD Drakos St. George Church Adrianopole place 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.: F D67 City : Karlsruhe Country : Germany Table Person First name : Martin Last name : Doerr Passport Nr.: 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 Dörr is identified by E72 Actor Appellation Martin Doerr is identified by E72 Actor Appellation F D67 is identified by E72 Actor Appellation is identified by E45 Address Karlsruhe, Germany has contact point E45 Address Heraklion, Greece has contact point real world equivalents 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 Field Knowledge 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 p Cultural repositories need an o-o “global schema” u As intermediate data format (“where data come together”) u As reasoning component – to settle differences u As adequate expression of the domain knowledge p Object-oriented semantic models are: u Adequate u State-of-the-art core components of repositories u Standard (e.G. RDFS) u Can be implemented on conventional platforms

ICS – FORTH, August 31, 2000 Requirements for Cultural Repositories (Apologies for the computer jargon) p Object-oriented core features needed: u object identity m value independent, perpetual, u types and classes m user defined, meaning bound, extensible u class or type hierarchy m multiple levels of abstraction m inheritance of properties u explicit representation of properties u extensibility m new subclasses, properties on existing body of data m keeping up-to-date with an open world

ICS – FORTH, August 31, 2000 Conclusions p Object-oriented semantic models (domain ontologies) are adequate to create cultural repositories p They must be product of interdisciplinary work, a valid expression of expert knowledge! p The CIDOC Conceptual Reference Model is such a model !