• What is a Component Diagram in UML?
• Component Diagram Notations
  • Component
  • Component Interfaces
  • Component Assemblies
  • Port
• When to Draw Component Diagram
• How to Draw Component Diagram?
• Component Diagram Examples

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What is a Component Diagram in UML?

The main purpose of a component diagram is to show the structural relationships between the components of a system. In UML, Components are made up of software objects that have been classified to serve a similar purpose. Components are considered autonomous, encapsulated units within a system or subsystem that provide one or more interfaces. By classifying a group of classes as a component the entire system becomes more modular as components may be interchanged and reused. Component diagrams document the encapsulation of the component and the means by which the component interacts via interfaces.

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Component Diagram Notations

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When to Draw Component Diagram?

1. Use component diagrams when you are dividing your system into components and want to show their interrelationships through interfaces.
2. The breakdown of components into a lower-level structure.

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How to Draw a Component Diagram?

1. Decide on the purpose of the diagram
2. Add components to the diagram, grouping them within other components if appropriate
3. Add other elements to the diagram, such as classes, objects and interface
4. Add the dependencies between the elements of the diagram

You can also:

1. Draw subsystems for logical categorization of components
   

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Component Diagram examples

Order Processing System Component diagram example

One main benefit of Component diagrams if to simplify the high-level view of the system. The Figure below is a much larger view of what is involved in a online store. By using a component diagram we see the system as a group of nearly independent component or subsystems that interact with each other in a specifically defined way.

Each component is responsible for the action for which it is named and interface(s) it provides. As long as those requirements are maintained changes to one component will not percolate to other components.

Ticket Selling System Component Diagram Example

There is a ticket seller component that sequentializes requests from both ticket selling system and clerks. A component that processes credit card charges; and the database containing the ticket information.

Component Example - Store Component - nested component structure

To show a nested component structure, you merely draw the component larger than normal and place the inner parts inside the name compartment of the encompassing component. The Figure below show's the Store's component nested structure.

Component Diagram Example - White-Box View of a Component

In the previous examples, those component diagrams are called black-box views. Ports are shown as squares bordering the component, these indicate how the interfaces of the component are used internally. Objects implementing a required interface are received via a port and objects implementing a provided interface are shared via a port.

In this example, the internal composition of components can also be modeled using component diagrams, this is called a white-box view of the diagram because we can see inside.

1. Ports are shown as squares bordering the component, these indicate how the interfaces of the component are used internally.
2. Objects implementing a required interface are received via a port and objects implementing a provided interface are shared via a port.

Component Diagram Example - Components in Deployment Diagram

Models the physical deployment of software components with UML deployment diagram. In deployment diagram, hardware components (e.g. web server, mail server, application server) are presented as nodes, with the software components that run inside the hardware components presented as artifacts.