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Difference between Dependency and Association

Sai Swami
Ranch Hand

Joined: Sep 24, 2002
Posts: 51
Hi Talented Ranchers,

Can anyone tell me the difference between Dependency and Association in class diagrams ?

Thanks for your time,
Punit Singh
Ranch Hand

Joined: Oct 16, 2008
Posts: 952
I think there are two types of Association : 1) Aggregation 2) Composition

1) Aggregation : I think you can think Aggregation part as Dependency. When a Car class need Tyres , and these tyres are provided to Car constructor from outside when constructing the Car object, then your Car class is dependent on the car list.
As in this example client of Car has to pass tyreList to its constructor.

2) Composition : When your Car class need not its client to pass anything to it, means you Car class will make its tyres itself, then it is using Composition. Here different types of dependency used, here Car is dependent on the Tyre class, not on its Client class to provide him tyres. So you can say Aggregation are more dependent on its client and tyres. While composition is not dependent on its client.

I think Association uses Dependency to work. So Association is the client of Dependency, think without any type dependency how Association will work?

Sai Swami
Ranch Hand

Joined: Sep 24, 2002
Posts: 51
I got the answer from ThoughtWorks web site:

Dependency is a loose form of Association. It is "optional" to show dependency in class diagrams. It is represented by a dotted arrow.

Thanks for the answer anyways,
Consider Paul's rocket mass heater.
subject: Difference between Dependency and Association