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classumldiagram

Interpreting the Difference in a UML Diagram of Three Classes in a Row versus Sharing a "Line"

I want to understand the difference between connecting classes together with a shared line or by having classes only "connect" through other classes. Is there a significant difference here? If classes share a line are you specifically trying to convey that information is being accessed from each of the other classes on the shared line?

For "Three Objects in a Row" I mean a layout that would appear as follows (sorry my diagram is: enter image description here

For "Sharing Lines" I mean a layout that would appear as follows:

UMl Diagram Example

Solution

  • difference about access

    In the first case instances of Flat and instance(s) of Tenant know each other, and independently of that instances of Tenant and instances of LeaseAgreement know each other. Instances of Flat do not have direct access to instances of LeaseAgreement and instances of LeaseAgreement do not have direct access to instances of Flat, they can only access the other instances if Tenant offers these accesses whatever the way (method or public attribute).

    In the second case there is an association-class, instances of Flat and Tenant know each other more the corresponding instance of LeasingContract indicating how they are associated.

    difference about knowledge

    In the first case supposing the hidden multiplicity are not 1 a tenant having two rents is associated with two instances of Flat and two instances of LeaseAgreement but there is nothing in the given model allowing to link the right instance of LeaseAgreement with the right instance of Flat, that means the model as it is do not say for which flat a lease agreement was written.

    In the second case there is no ambiguity, each couple of instances Flat and Tenant is associated with (in fact throw) the right instance of LeasingContract