Depicting association between list and a class inside this list in UML

Question

I'm making an UML class diagram representing classes used for authentication.

There are 3 classes:

• X509AuthenticationFilter
• ProviderManager
• X509AuthenticationProvider

The X509AuthenticationFilter HAS a ProviderManager.

The ProviderManager HAS a List<AuthenticationProvider>

And in this list that the manager has there's the X509AuthenticationProvider alongside with other AuthenticationProvider's

My question is about how to display such a relation between the ProviderManager and the X509AuthenticationProvider?

The best I could come up with is just a simple association like below:

But I still do have second thoughts... Maybe there's a standard for displaying such a relationship?

Answer 1

Indeed, a simple association seems the best way to represent this relationship. You may consider indicating a * multiplicity.

What about the alternatives ?

• It seems that UML composition (black diamond) is not suitable, considering that composition implies responsibility for the lifecycle of the components, whereas your constructor suggest that the list and its elements could be used somewhere else. (btw, you’d consider adding a « Create » before your constructor)

• You could consider shared aggregation (white diamond), but I would not advise it: although very popular for expressing a “HAS A” relationship, the UML specification leave its semantic unspecified, and the UML founders called it a “modeling placebo”. It has no advantage to use it over a simple association, unless you work in the context of a team that defined a context-specific semantic.

If you’re in UML hardcore you could consider using the dot notation at the end of the arrow, in addition to your current notation.

Answer 2

For more completeness, and since AuthenticationProvider is the Base, you may consider

• an association with multiplicity (*) from ProviderManager to AuthenticationProvider
• Show a derived relation between AuthenticationProvider and X509AuthenticationProvider
• Show a direct association from ProviderManager to X509AuthenticationProvider