Basic Modelling Concepts

Modelling tools have their own interpretation of how diagrams, icons are used. This webpage tries to give some clues on how this implementation are made.

Diagram Elements	Sterotypes
Class Diagram Elements Class Diagram Elements	Standard Icons Stereotypes. Standard Icons Stereotypes.

Object Orientation Basic Elements

Basic OO Elements are:

• Associaton
• Aggregation
• Composition

Association

https://upload.wikimedia.org/wikipedia/en/f/f5/BidirectionalAssociation.png	https://upload.wikimedia.org/wikipedia/en/0/05/UnidirectionalAssociation.png
A bidirectional association	Unless otherwise specified, navigation across an association is bidirectional, although it may be limited to just one direction by adorning some end with an arrowhead pointing to the direction of traversal.
Description
Association defines a relationship between classes of objects that allows one object instance to cause another to perform an action on its behalf.

Aggregation

https://upload.wikimedia.org/wikipedia/commons/d/d0/Aggregation-Composition3.png
A bidirectional association, first a composition, the second is an aggregation.
Description
Association defines a relationship between classes of objects that allows one object instance to cause another to perform an action on its behalf. A "uses" B = Aggregation : B exists independently (conceptually) from A. Example: A Company is an aggregation of People. A Company is a composition of Accounts. When a Company ceases to do business its Accounts cease to exist but its People continue to exist.

Composition

1-directional composition
Description
A "owns" B = Composition : B has no meaning or purpose in the system without A. The arrowhead on the other end of the relationship denotes that the relationship is navigable in only one direction. That is, Point does not know about Circle. Example: Each instance of type Circle contains instance(s) of type Point. A Text Editor owns a Buffer (composition). A Text Editor uses a File (aggregation). The university has faculties which exists on its departments (composition). Departments uses employees/members (aggregation).

In Java:

public class Point { private float x; private float y; /** * Constructor * @param x Value for the x-axis. * @param y Value for the y-axis. */ public Point(float x, float y) { this.x = x; this.y = y; } ... }

width="525" public class Circle { private float radius; private Point center; /** * Constructor * @param center Instance of class point * @param radius Length of the radius. */ public Circle(Point center, float radius) { this.center = center; this.radius = radius; } ... }

Class Diagrams

Als een associatie

• Attributen heeft
• Operaties heeft
• Associaties heeft met andere classes

Introduceer dan een associatie class!

Ontwerpbeslissingen	Development design decisions
- 1 -
Attributen zijn private Getters en Setters toevoegen (Alleen indien nodig)	Attributes are private Add only the necessary Getters and Setters
- 2 -
Constructor heeft parameters: Identificerende attributen Verplichte attributen Optioneel extra constructors Indien vaak meer parameters gewenst zijn.	Constructor has parameters: Identifying attributes Required attributes Optional extra (alternative) constructors When often more parameters are required
- 3 -
Associatie met lage multipliciteit Kies één of meer attributen van enkelvoudig type Associatie met hoge multipliciteit Kies voor een attribuut van type Collection	Association with low multiplicity Choose one or more attributes of base type Association with high multiplicity Choose an attribute of type Collection
- 4 -
Afleidbare informatie Definieer een functie om de waarde te berekenen (of sla de waarde op in een attribuut). Vermijd redundantie	Derivable / deductable Information Define a method to calculate the value (or use an attribute)
- 5 -
If an association has Attributes Operations / Methods Associations with other classes Then Introduce an association class.
- 6 -
Administratieve verplicting Bij een aggregatie kunnen onderdelen van een object zelfstandig blijven voortbestaan Bij een compositie verdwijnen onderdelen van een object als het betreffende object verdwijnt levensduur onderdeel ≤ levensduur object
- 7 -
Liskov substitutieprincipe: Overal waar een instantie van een class gebruikt kan worden, kan ook altijd een willekeurige instantie van een willekeurige subclass of subtype gebruikt worden	Barbara Liskov: Let q(x) be a property provable about objects x of type T. Then q(y) should be provable for objects y of type S, where S is a subtype of T.
- 8 -
Programmeer tegen een interface, niet tegen een implementatie	Program to an interface, not against an implementation

See also

http://agilemodeling.com/images/style/classDiagramAnalysisVsDesign.gif

• Agile Modeling, Class Diagrams Guidelines. See example above.