Inside one class there is another nested member class.
What to use in this case:

Composition (filled diamond) or Containment (circle with a plus)?

UML generators from code use Containment, and the teacher uses Composition with the qualifying word "Contain".

And why cannot the Containment notation be used in Visio 2016?

    1 answer 1

    From English Wikipedia :

    There are several instances of composited data. Examples of such containers are arrays, associative arrays, binary trees, and linked lists.

    In the UML, it is not necessary to identify the data type.

    If in Russian:

    Content ( Containment ) is a composition subspecies ( Composition ) that is used to store a variety of instances of stored data. Examples include arrays, linked lists, dictionaries.

    In UML, the content ( Containment ) is indicated by a relationship with a multiplicity of 1 or 0..n (depending on the particular case), indicating that one data type is stored in another with a previously unknown numeric instance.

    That is, the content is called a composition, where the number of dependent instances may be indefinitely large.

    In the UML specification itself, Containment is not isolated separately from Composition; probably, the mentioned notation is not official. However, the diagrams serve to simplify the understanding of the essence of the program, therefore some details may vary within reasonable limits, and both options described by the author of the question may be relevant.

    • one
      One reservation, the site uml-diagrams.org itself is not a specification, although the site itself is very good and IMHO reveals the spirit of this ... - Fat-Zer
    • UML specification group omg.org Object Management Group. They train and issue certificates on UML of various versions. - Vyacheslav Mischenko