UML Aggregation with and without arrow head

Question

I always thought that the UML aggregate is defined as a black (filled) diamond at the beginning of a path and no arrow head that the end:

|--------|        |         


        

Answer 1

Direction implies a client/server or master/slave relationship. In the case of aggregation, the usual situation is the programmer uses the aggregate to find the sub-components for that object (e.g., use the car to find the car parts). Directionality towards the part class makes this relationship explicit, though in most cases it is redundant.