The domain model shows the structure of the PBAS and defines the internal interactions between each component. Every component and actor of the system is represented by a box with its attributes and operations encapsulated inside it. Relationships between components are shown as links and the purpose of the link is detailed. Each component is an aggregate part of the PBAS system, therefore all components are linked to the main PBAS class by the diamond tipped link. Figure \ref{fig:ClassDomain} shows the model followed by its data dictionary. The data dictionary describes each actor and component and their attributes and operations.