I have the following sequence diagram to add a student to a list of students. the implementation could be like

List<Student> Students = new List<Student>();

I drew the following sequence diagram for it:

enter image description here

In this diagram Students is actually the list of students mentioned in the code.

I would like to know is it a correct way to show a list of objects as a object lifeline? I mean as a conceptual and analysis approach and also at syntax.

For example maybe the List<Student> could be the object of a general class named Storage which is responsible to store and retrieve a list of objects like a database...

1 Answer 1


Description of lifeline from UML 2.4.1 standard:

A Lifeline is shown using a symbol that consists of a rectangle forming its “head” followed by a vertical line (which may be dashed) that represents the lifetime of the participant. Information identifying the lifeline is displayed inside the rectangle in the following format:

<lifelineident> ::= ([<connectable-element-name>[‘[‘ <selector> ‘]’]] [: <class_name>] [decomposition]) | ‘self’
<selector> ::= <expression>
<decomposition> ::= ‘ref’ <interactionident> [‘strict’]

So, you should rename Students to Students : List<Student> or just :List<Student>. The part after colon (:) represents a type (<class_name> from notation above).

There is no special syntax for representing lists.

EDIT: as for "Student Storage/Adapter"

If List does the job, just use it. It is object-oriented enough as it is. No need to introduce a pattern for the sake of introducing a pattern, and more than so for the sake of writing a busy-sounding class name to a diagram. Keep it simple.

  • I drew it in Visio, for example the class of Form1 is Form but it didn't show it, anyway thank you! but still I didn't get is it a right way to use a list or not! I mainly mean at conceptual analysis and not necessarily syntax
    – Ahmad
    Commented Nov 23, 2014 at 8:29
  • That is OK at conceptual level too. Your list is a valid participant of a process, and it doesn't really matter if it's a list or something else anyways - it a sequence diagram, not class diagram.
    – scriptin
    Commented Nov 23, 2014 at 8:32
  • Could we say its actually a class like StudentAdapter or ... which is responsible to keep the list of students or save them in a database or ... So maybe its better to have a class for it where the storage is not specified and manipulation to the storage are shown? I modified my question to add that.
    – Ahmad
    Commented Nov 23, 2014 at 8:46

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