Use Case Modelling

• Use Case Modelling is a very popular technique to find out user requirement
• Use cases describe the system from the user's point of view
• A use case defines the interactions between external actors and the system under consideration to accomplish a goal
• It describe the interaction between one or more actors and the system itself represented as a sequence of simple steps
• There are main formats used to express use cases: High-Level format and Expand format
• A High-Level use case describes a process very briefly. This format is typically useful during the early stages of a development project.
• An Expanded use case describes a process in more detail than a high level description. An expanded use case description includes a step by step description includes a step by step description of the typical course of events for the use case. It is sometimes useful during requirements gathering and analysis.
• A use case defines a sequence of actions performed by a system that yields and observable result of value to an actor
• A use case is always initiated by an actor
• A use case provides value to an actor
• A use case is complete

The Actor

An actor is usually drawn as a named stick figure, or alternatively as a class rectangle with the keyword

• What is an actor?
• Not part of the system
• Represents roles a user can play
• Represents human a machine or another system
• Activity exchange information with the system
• A give or a recipient
• Who will use the system?
• Who will maintain the system?
• What hardware does the system support or interact with?
• What other systems are needed for this system to work?
• Who will supply, use, or remove information?
• Who create it?
• Who displays or uses it?
• Who delete it?
• For each actor, ask the following questions
• What are the primary tasks the actor wants the system to perform>
• Will the actor create, store, change, remove, or read data in the system?
• Will the actor need to inform the system about sudden, external changes?
• Will the actor perform a system startup or termination?