SYSTEM MODELLING:
System modeling is the process of developing abstract models of a system, with each model presenting a different view or perspective of that system. It is about representing a system using some kind of graphical notation, which is now almost always based on notations in the Unified Modeling Language (UML). Models help the analyst to understand the functionality of the system; they are used to communicate with customers.
Models can explain the system from different perspectives:
• An external perspective, where you model the context or environment of the system.
• An interaction perspective, where you model the interactions between a system and its environment, or between the components of a system.
• A structural perspective, where you model the organization of a system or the structure of the data that is processed by the system.
• A behavioral perspective, where you model the dynamic behavior of the system and how it responds to events.
Five types of UML diagrams that are the most useful for system modeling:
• Activity diagrams, which show the activities involved in a process or in data processing.
• Use case diagrams, which show the interactions between a system and its environment.
• Sequence diagrams, which show interactions between actors and the system and between system components.
• Class diagrams, which show the object classes in the system and the associations between these classes.
• State diagrams, which show how the system reacts to internal and external events.
Models of both new and existing system are used during requirements engineering. Models of the existing systems help clarify what the existing system does and can be used as a basis for discussing its strengths and weaknesses. These then lead to requirements for the new system. Models of the new system are used during requirements engineering to help explain the proposed requirements to other system stakeholders. Engineers use these models to discuss design proposals and to document the system for implementation.
