A composite structure diagram is a diagram that shows the internal structure of a classifier, including its interaction points to other parts of the system. It shows the configuration and relationship of parts that together perform the behaviour of the containing classifier.
Class elements have been described in great detail in the section on class diagrams. This section describes the way that classes can be displayed as composite elements exposing interfaces and containing ports and parts.
A part is an element that represents a set of one or more instances which are owned by a containing classifier instance. So for example, if a diagram instance owned a set of graphical elements, then the graphical elements could be represented as parts, if it were useful to do so to model some kind of relationship between them. Note that a part can be removed from its parent before the parent is deleted, so that the part isn't deleted at the same time.
A part is shown as an unadorned rectangle contained within the body of a class or component element.
A port is a typed element that represents an externally visible part of a containing classifier instance. Ports define the interaction between a classifier and its environment. A port can appear on the boundary of a contained part, a class or a composite structure. A port may specify the services a classifier provides as well as the services that it requires of its environment.
A port is shown as a named rectangle on the boundary edge of its owning classifier.
An interface is similar to a class but with a number of restrictions. All interface operations are public and abstract, and do not provide any default implementation. All interface attributes must be constants. However, while a class may only inherit from a single super-class, it may implement multiple interfaces.
An interface, when standing alone in a diagram, is either shown as a class element rectangle with the «interface» keyword and with its name italicised to denote it is abstract, or it is shown as a circle.
Note that the circle notation does not show the interface operations. When interfaces are shown as being owned by classes, they are referred to as exposed interfaces. An exposed interface can be defined as either provided or required. A provided interface is an affirmation that the containing classifier supplies the operations defined by the named interface element and is defined by drawing a realisation link between the class and the interface. A required interface is a statement that the classifier is able to communicate with some other classifier which provides operations defined by the named interface element and is defined by drawing a dependency link between the class and the interface.
A provided interface is shown as a "ball on a stick" attached to the edge of a classifier element. A required interface is shown as a "cup on a stick" attached to the edge of a classifier element.
A delegate connector is used for defining the internal workings of a component's external ports and interfaces. A delegate connector is shown as an arrow with a «delegate» stereotype. It connects an external contract of a component as shown by its ports to the internal realisation of the behaviour of the component's part.
A collaboration defines a set of co-operating roles used collectively to illustrate a specific functionality. A collaboration should only show the roles and attributes required to accomplish its defined task or function. Isolating the primary roles is an exercise in simplifying the structure and clarifying the behaviour, and also provides for re-use. A collaboration often implements a pattern.
A collaboration element is shown as an ellipse.
A role binding connector is drawn from a collaboration to the classifier that fulfils the role. It is shown as a dashed line with arrowhead and the stereotype «role binding».
A represents connector may be drawn from a collaboration to a classifier to show that a collaboration is used in the classifier. It is shown as a dashed line with arrowhead and the stereotype «represents».
An occurrence connector may be drawn from a collaboration to a classifier to show that a collaboration represents(sic) the classifier. It is shown as a dashed line with arrowhead and the stereotype «occurrence».
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