UMLR — Section: 16.3.5

The Description section states: "Note that the included use case is not optional, and is always required for the including use case to execute correctly." This is often understood as stating that the behavior of an included use case has to be executed during every execution of the behavior of the including use case. Example: The following informal use case fragment contains a conditional call of an included use case: Step x: If the user choses to print the reports, <<include>> the use case "Print reports". With the understanding given above, this use case fragment would be invalid (at least if the included use case is not included elsewhere in the including use case). In a similar vein, the Semantics section states: "All of the behavior of the included use case is executed at a single location in the included use case before execution of the including use case is resumed." Besides the obvious error (the sentence should say: "... is executed at a single location in the including use case ..."), this is sometimes understood as stating that the behavior of the included use case must be executed exactly once during the execution of the including use case. Another (equally wrong) interpretation would be that the included use case must be included exactly once in the use case specification (implying, for example, that there must not be two lines in the same textual use case specification containing an <<include>> directive for a certain use case). Both sections should be clarified, clearly stating that: - The behavior specification of the including use case may include an included use case multiply (although this is represented by a single include relationship in the use case diagram). Analogy: A routine that contains multiple calls to a subroutine in its source code. - The including use case is responsible for calling the included use case. It may choose to call it once, repeatedly, or not at all. Analogy: A routine with conditional execution paths or iterative behavior, performing subroutine calls conditionally or iteratively. Proposal for changing the sentence in the Description section: "Note that the included use case is not optional, and is always required for the including use case to be fully specified. The behavior specification of the including use case may include an included use case multiply (although this is represented by a single include relationship in the use case diagram)." Proposal for a change and an addition in the Semantics section: "All of the behavior of the included use case is executed in the including use case before execution of the including use case is resumed. Depending on behavior of the including use case, the included use case may be called once, multiple times or not at all." I would be very pleased to receive a first, quick reply by mail.