Elaboration

Elaboration

1. Defining classes, data and system structure

   • coupling is bad, too many dependencies
   • cohesion is good, each class has single well defined job

2. ER (Enitity-Relation) diagrams, old style

   • entities in boxes
   • relation in diamonds
   • roles showed by links

3. Class Diagram

   • class represented by box separated into 3 boxes, first for name, second for attributes, third for operations
     • attributes given a type (name : String) and visibility
       • + public, # package, ~ protected, - private
     • operations given signature and type (print(s : String) : void) and visibility
   • Association between classes (-has-a-) shown by solid line with cardinality at each end
     • Composition means the object dies at the same time as the thing having the object, shown by an filled in diamond at the "haver's" end.
     • Aggregation means the object may live on and be reused, shown by an open diamond at "haver's" end
     • Associations can be given roles, like a Person can be a member in a Department, or a manager. Associations can then subset each other, as a manager is still a member. subsetting is shown with a dashed arrow pointing at that being subsetted, with "{subset}" written above.
   • Generalisation (-is-a-) shown by solid line and empty arrow head pointing to parent
   • Methods in classes may be dependent on other classes, in which case a dashed line is drawn between the method/field and the class, with the arrow head pointing at what is being depended on.
   • Interface shown as open circles with name underneath and association line between them and implementing classes

4. class design may come from CRC cards, with each card mapping to a class, collaborations revealing associations etc and responsibility revealing attributes and operations