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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 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: Museum Artefact type Holy Bread Basket museum number TA 153 collection Byzantine material silver O-O Schema declaration (Classes): Museum Artefact O-O Schema usage (Instances): Holy Bread Basket museum number museum number TA 153 collection collection Byzantine material material silver Ecclesiastical item belongs to church belongs to church St. George of Andranopole container container TA 153’container lid lid TA 153’lid Holy Bread Basket ICS – FORTH, August 31, 2000 More Advanced Features: Multiple Inheritance (multiple higher terms) Single Inheritance form: Multiple Inheritance form: Museum Artefact Canister museum number museum number collection collection material material Ecclesiastical item container lid Museum Artefact belongs to church Holy Bread Basket Ecclesiastical item Canister container lid belongs to church Holy Bread Basket container lid Repetition of properties ! ICS – FORTH, August 31, 2000 Unique identity of properties ! Problem of Global Searches: Identity of property Artefact Action Holy Bread Basket TA 153 Commemoration of Drakos belongs to Holy Bread Basket Offered Object belongs to Commemoration container TA 153’container date 1667 AD lid TA 153’lid place Adrianopole Drakos subject Drakos St. George Church commemorating donator notion of action hidden ! acceptor notion of action explicit Holy Bread Basket TA 153 belongs to Holy Bread Basket Offered Object Drakos’offer belongs to Offer date 1667 AD container TA 153’container place Adrianopole lid TA 153’lid subject Drakos offer Drakos’offer acceptor St. George Church normalized form 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 ICS – FORTH, August 31, 2000 ? ? Who am I ? Object-orientated Semantic Models: Separating Identity From Description real world equivalents persistent identifiers fully qualified entities E21 Person E72 Actor Appellation * is identified by Martin Dörr E72 Actor Appellation is identified by Martin Doerr is identified by E72 Actor Appellation F5630288D67 is identified by E72 Actor Appellation 3515020669 E45 Address has contact point Karlsruhe, Germany E45 Address ICS – FORTH, August 31, 2000 has contact point Heraklion, Greece Object-orientated Semantic Models: Multiple Instantiation E72 Actor Appellation Martin Doerr Illness Type Paradontosis Research Field is identified by suffers from Patient Researcher * is interested in Farmer Knowledge Representation cultivates Crop Type Olives 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 ! ICS – FORTH, August 31, 2000
