composition | has definition A strong kind of aggregation in which if the aggregate is destroyed, then the parts are destroyed as well | |
has example The rooms of a building cannot exist without the building | |
is a subtopic of 5.6 - More Advanced Features of Class Diagrams | |
is drawn as a solid (filled-in) diamond in a UML diagram | |
is a kind of aggregation | |
aggregation | represents 'part-whole' relationships | |
association | can have a label which is an association name or a role name | |
describes a relationship that will exist between instances at run time | |
has default name "has" if it has neither an association name nor a role name | |
has part association name | |
has part role name | |
is bi-directional unless it has an arrow at one end indicating directionality | |
is legitimate only if its links will survive beyond the execution of any particular operation | |
is usually implemented using instance variables in Java: you divide each two-way association into two one-way associations - so each associated class has an instance variable | |
may be implemented in several ways in Java | |
must not be added to a model unless it is relevant to the application - it will be needed to implement some requirement | |
should exist if a class possesses, controls, is connected to, is related to, is a part of, has as parts, is a member of, or has as members, some class in your model | |
should have sufficient names to make the association clear and unambiguous | |
shows how two classes are related to each other | |
data abstraction | groups the pieces of data that describe some entity, so that programmers can manipulate that data as a unit | |
helps a programmer to cope with the complexity of data | |
hides the details of data | |