Question

How can I indicate that a method will return a collection of objects in UML? Is there a better way to explain the relationship than to have a collection class as a return type?

Answer 1

You may consider to use an “association”. There are three basic types of association: composition, aggregation and “normal” association. Each of them expresses a different existential dependency of the whole to the part and vice versa.

Usually associations are expressed by connecting two classes by a line. Composition and aggregation have a diamond symbol at the composite’s/aggregate’s side. The composite/aggregate consists of one or more parts. (See the wiki-article)

Example:

Immagine you have two classes: Library, Book. We can say the Library is the whole and Book the part. We could notate it like this (in ASCII, please google for real diagrams).

Library (Aggregate) <>— Book (Part)

If you want to express these relationships association will be your friend.

EDIT:

As I said in the comment, I don’t think there is a special notation for returned collections. However, you’re right, returning a Collection is kinda language specific. But you may consider to return an array (String[]), which is a more general way to represent a set of values and should be more language independent than a Collection. It’s then up to the programmer how he implements it. He may use a Collection, a C++ STL vector … the point is: return a set of values.