Geoinformation Technology: lecture 2 (b) Object Modeling

1. Geoinformation Technology: lecture 2 (b)Object Modeling Prof. Dr. Thomas H. Kolbe Institute for Geodesy and Geoinformation Science Technische Universität Berlin Credits: This material is mostly an english translation of the course module no. 2 (‘Geoobjekte und ihre Modellierung‘) of the open e-content platform www.geoinformation.net.

2. Object-orientation: Generalization  Specialization • Abstraction principle for the hierarchical structuring of a model • a specialized class concretises a more generalclass by adding specific properties; • the general class is called superclass, the specialized class subclass; • one superclass can have different subclasses • also: one subclass can have different superclasses (alsocalled parent classes) general class specialization generalization specialized class

3. OO: Example #1 for generalization, specialization • „staff_member“ is a more general concept as „non_ research_associate“, „research_associate“ or „professor“ • „staff_member“ is the superclass • „non_ research_associate“, „research_associate“, and „professor“ are subclasses staff_member non_ research_associate research_associate professor

4. OO: Example #2 for generalization, specialization • „geometrical figure“ is a more general concept than „triangle“, „circle“ or „rectangle“ geometrical figure triangle circle rectangle

5. Object-orientation: Taxonomy • generalization and specialization describe a taxonomical(i.e. systematic) relationship between general and specific concepts Example: Taxonomy of flies with two wings (from biology) Orthorrhapha Brachycera - flies Cyclorrhapha Diptera – Flies (with two wings) Aschiza Schizophora Nematocera - mosquito Acalyptratae Calyptratae

6. Object-orientation: Aggregation vs. Generalization • What is the difference between an aggregation and a generalization? • aggregation and generalization build hierarchies, but : • aggregation relates objects • generalization relates classes • Please note the systematic difference between following relationships • University – Faculty (aggregation of objects) • Rectangle – Figure (generalization of the same object)

7. Object-orientation: Inheritance and specialization (I) • A superclass represents a concept. • A subclass specializes this concept, such that that it • explicitlyadopts the attributes of the superclass • Inheritance of properties • explicitly adopts or overrides methods of the superclass • Inheritance of the behavior • defines new attributes • defines new methods

8. Object-orientation: Example #1 for Inheritance student staff member • name • first name • registration number • - subject • address • date of birth • registration-date • Bachelor • Master • name • first name • personnel number • - institute • address • date of birth • bank account no. • salary

9. Object-orientation: Example #1 for Inheritance person • name • first name • - address • - date of birth student staff member • - registration number • - subject • registration-date • . . . • personnel number • - bank account no. • salary • . . .

10. Object-orientation: Example #2: Overriding geometrical figure • center: Point • visible: Boolean +display ( ) +delete ( ) +move ( ) triangle circle rectangle • radius: number • a: number • b: number • c: number • a: number • b: number +display ( ) +delete ( ) +display ( ) +delete ( ) +display ( ) +delete ( )

11. Object-orientation: Inheritance and specialization (II) • subclasses differ systematically wrt. each other • attributes and methods of a class represent a self-contained concept • the specialized class is fully compatible to the general class • attributes and methods of the superclass do not have to be repeated in the specification of the subclass(es) geometrical figure • center: Point • visible: Boolean +display( ) +delete( ) +move( ) triangle circle rectangle • radius : number • a: number • b: number • c: number • a: number • b: number +display( ) +delete( ) +display ( ) +delete ( ) +display ( ) +delete ( )

12. Object-orientation: Polymorphism • congeneric (similar) methods, that are to be executed on objects of different classes, can be named with the same identifier • when calling such a method, the (most) object-specific one is activated in each case • advantage of the polymorphism: specific objects can be handled in a general way • triangles, circles, and rectangles can be treated as geometrical figures geometrical figure • center: Point • visible: Boolean +display ( ) +delete ( ) +move ( ) triangle circle rectangle • radius : number • a: number • b: number • c: number • a: number • b: number +display ( ) +delete ( ) +display ( ) +delete ( ) +display( ) +delete( )

13. Example #2 with spatial reference

14. Example #2: state - district - municipality - parcel state district • name: string • inhabitants: number • area: number 1..* • name: string • inhabitants: number • area: number +getname( ): string +getinhabitants( ):number +getarea( ): number +getname( ): name +getinhabitants( ):number +getarea( ): number Declare the multiplicities Name the relationships Declare the methods Declare the attributes property municipality • owner: Person • area: number • name: string • inhabitants: number • area: number 1..* 1..* +getowner( ): Person +getarea( ): number +getname( ): string +getinhabitants( ):number +getarea( ): number

15. Example #2: property - parcel - polygon • Can this subdivision of space can be extended further than "property"? • at first: • transition from the legal object "property" to the geometrical object "polygon" 1 . . n property parcel polygon geometry

16. Example #2: Topological relationships of polygons bounds node edge bounds face

17. Example #2: polygon – edge – node - point 1..2 3 . . * polygon edge  bounds 2 . . * Declare the multiplicitys and names Name the relationships  bounds 2 1 1 geometry point node

18. Example #2: Class ‘point‘ point • latitude: degree • longitude: degree • X: number • Y: number • projection: text • registration: text=“GPS“ • registration-date: date + getlatitude( ) : degree + getlongitude( ) : degree + setlatitude(lat: degree) + setlongitude(lon: degree) + getX( ) : number + getY( ) : number + . . .

19. Data Modelling Literature • Balzert, Heide: Lehrbuch der Objektmodellierung. Akademischer Verlag, 1999 • Oestereich, Bernd: Objektorientierte Softwareentwicklung: Analyse und Design mit der Unified Modeling Language. 4. Auflage - Oldenbourg, • München Wien, 1998 • (english titles will be added soon)