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:

• 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
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

A one directional Composition
Description
A "owns" B = Composition : B has no meaning or purpose in the system without A. Example: Each instance of type Circle contains an instance of type Point.

Example:
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).

See also

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

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