Course Map

Agenda

• Composite Structure Diagrams
• What is a Component?
• Component Notation
• White Box Components
• Internal Component Classifiers
• Ports and Combing Other Components
• Components and Dependencies
• Architectural Analysis - Find Packages
• Architectural Design - Design a Subsystem

What is a Component?

• A component is a self contained unit that encapsulates the state and behavior of a number of classifiers. A component specifies a formal contract of the services that it provides to its clients and those that it requires from other components or services in the system in terms of its provided and required interfaces.
• A component is a substitutable unit that can be replaced at design time or run-time by a component that offers equivalent functionality based on compatibility of its interfaces. As long as the environment obeys the constraints expressed by the provided and required interfaces of a component, it will be able to interact with this environment. Similarly, a system can be extended by adding new component types that add new functionality.
• The required and provided interfaces of a component allow for the specification of structural features such as attributes and association ends, as well as behavioral features such as operations and events. A component may implement a provided interface directly, or, its realizing classifiers may do so. The required and provided interfaces may optionally be organized through ports, these enable the definition of named sets of provided and required interfaces that are typically (but not always) addressed at run-time.
• A component has an external view (or “black-box” view) by means of its publicly visible properties and operations. Optionally, a behavior such as a protocol state machine may be attached to an interface, port, and to the component itself, to define the external view more precisely by making dynamic constraints in the sequence of operation calls explicit. Other behaviors may also be associated with interfaces or connectors to define the ‘contract’ between participants in a collaboration (e.g., in terms of use case, activity, or interaction specifications).
• The wiring between components in a system or other context can be structurally defined by using dependencies between component interfaces (typically on structure diagrams). Optionally, a more detailed specification of the structural collaboration can be made using parts and connectors in composite structures, to specify the role or instance level collaboration between components (See Chapter Composite Structures).
• A component also has an internal view (or “white-box” view) by means of its private properties and realizing classifiers. This view shows how the external behavior is realized internally. The mapping between external and internal view is by means of dependencies (on structure diagrams), or delegation connectors to internal parts (on composite structure diagrams). Again, more detailed behavior specifications such as interactions and activities may be used to detail the mapping from external to internal behavior.

Component Notation

• A component is shown as a Classifier rectangle with the keyword «component». Optionally, in the right hand corner a component icon can be displayed. This is a classifier rectangle with two smaller rectangles protruding from its left hand side.
• Black box notation

The ball-and-socket notation. A Component with two provided and three required interfaces

• Alternatively, the interfaces and/or individual operations and attributes can be listed in the compartments of a component box (for scalability, tools may offer way of listing and abbreviating component properties and behavior).

Black box notation showing a listing of the properties of a component

• For displaying the full signature of an interface of a component, the interfaces can also be displayed as typical classifier rectangles that can be expanded to show details of operations and events.

White Box Components

• An internal, or white box view of a Component is where the realizing classifiers are listed in an additional compartment. Compartments may also be used to display a listing of any parts and connectors, or any implementing artifacts.
  
  A white-box representation of a component

Nested representation

Internal Component Classifiers

• The internal classifiers that realize the behavior of a component may be displayed by means of general dependencies. Alternatively, they may be nested within the component shape.
  
   

Ports and Combing Other Components

• Interfaces that are exposed by a Component and notated on a diagram, either directly or though a port definition, may be inherited from a supertype component. These interfaces are indicated on the diagram by preceding the name of the interface by a forward slash. An example of this can be found below, where “/OrderableItem” can be an interface that is implemented by a supertype of the Product component.
• A delegation connector is notated as a Connector from the delegating source Port to the handling target Part, and vice versa for required Interfaces or Ports.
• An assembly connector is notated by a “ball-and-socket” connection between a provided interface and a required interface. This notation allows for succinct graphical wiring of components, a requirement for scaling in complex systems.

Example of a platform independent model of a component, its provided and required interfaces, and wiring through dependencies on a structure diagram.

Component Assembly

In a system context where there are multiple components that provide or require a particular interface, a notation abstraction can be used that combines by joining the multiple connectors. This abstraction is similar to the one defined for aggregation and subtyping relationships.

As a notation abstraction, multiple wiring relationships can be visually grouped together in a component assembly.