问题
Tools allow to create a use dependency between an actor and a use case even if the meaning of a such dependency is not clear and if no such dependencies are described in the norm ?
回答1:
The answer contains two parts : one about the keyword << use >> and one about Dependencies usage.
Keyword: "UML keywords are reserved words that are an integral part of the UML notation and normally appear as text annotations attached to a UML graphic element or as part of a text line in a UML diagram." (page 743)
One usage of keyword is (page 743): "To distinguish a particular kind of relationship between UML concepts (meta-association) from other relationships sharing the same general graphical form. For example, dashed lines between elements are used for a number of different relationships, including Dependencies, relationships between UseCases and an extending UseCases, and so on."
The use keyword specifies an Usage dependency and an Usage dependency may be defined between two NamedElement.
Actor and UseCase are two NamedElement, so it is possible to model a << use >> dependency between an Actor and UseCase even if the meaning of a such relation is not clear and even if the specification said about Actor :"An Actor can only have Associations to UseCases, Components, and Classes. Furthermore these Associations must be binary."
来源：https://stackoverflow.com/questions/47181038/why-is-it-possible-to-model-a-use-dependency-between-an-actor-and-a-use-case