The P2P list 'has a' member, use Aggregation relation
a variant of the "has a" association relationship; aggregation is more specific than association. It is an association that represents a part-whole or part-of relationship. As a type of association, an aggregation can be named and have the same adornments that an association can. However, an aggregation may not involve more than two classes.
Aggregation can occur when a class is a collection or container of other classes, but where the contained classes do not have a strong life cycle dependency on the container — essentially, if the container is destroyed, its contents are not.
In UML, it is graphically represented as a hollow diamond shape on the containing class end of the tree with a single line that connects the contained class to the containing class.The aggregate is semantically an extended object that is treated as a unit in many operations,although physically it is made of several lesser objects...