UML: TIP: MagicDraw UML: unlike Package and Model, a Component does not always "steal ownership" of graphically contained elements.

The tool behavior described here for MagicDraw™ UML may or may not apply to your Unified Modeling Language™ (UML™) tool.

In MagicDraw™ UML, if you move a Class or Interface symbol in a diagram from outside the rectangular boundary of a Component's symbol to inside the Component's symbol that Component DOES NOT STEAL OWNERSHIP of the Class or Interface symbol.

(NB: In MagicDraw™ UML, if you move a Class or Interface in the model browser into a Component in the model browser, that Component DOES STEAL OWNERSHIP !)

This means that a Component can be used to "parasitically" logically and graphically "wrap" Classes, Interfaces (and certain other elements) in diagrams.

Also, a ComponentRealization relationship will be generated between the Class or Interface and the Component, which can be used to trace the "wrapping" of a given Class or Interface by possibly many «wrapper» Components.

The «wrapper» Component strategy is so powerful (and so useful for UML™ Parsing Analysis) that many of the Webel site UML examples are dedicated to illustrating it.

Please compare this strategy with the UML2.1.2 Model and PackageImport:

17.3.1 Model (from Models):

A model captures a view of a physical system. It is an abstraction of the physical system, with a certain purpose.

The Model construct is defined as a Package. It contains a (hierarchical) set of elements that together describe the physical system being modeled. A Model may also contain a set of elements that represents the environment of the system, typically Actors, together with their interrelationships, such as Associations and Dependencies.

A model owns or imports all the elements needed to represent a physical system completely according to the purpose of this particular model.

7.3.39 PackageImport (from Kernel):

A package import is a relationship that allows the use of unqualified names to refer to package members from other namespaces.

However, in MagicDraw™ UML there is no automated mechanism for generating a traceable PackageImport when an element symbol is moved in a diagram into a Model symbol in a diagram; rather, the Model "steals ownership" of the moved element.

Note also that the symbol for a Model has a little tab at the top, whereas a Component is a nice clean rectangle. This may seem trivial, however it makes it much easier to use nested Components than nested Models in diagrams for hierarchical logical and graphical wrapping.
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