Question

a) What is a use case? Describe what an “actor” is and what a “scenario” is in the context of use case.

b) What is a use case diagram? What is the purpose of a use case diagram as a tool for software engineering?

c) Draw a use case diagram for a simple Small Library Management System with requirements described below

Answer 1

a) A use case is the primary form of system/software requirements for a new software program under developed. Use cases specify the expected behaviour , and not the exact method of making it happen . Use cases once specified can be denoted both textual and visual representation . A key concept of use case modeling is that it helps us design a system from end user's perspective. It is an effective technique for communicating system behavior in the user's terms by specifying all externally visible system behavior.

A use case involves an actor and the flow that a particular actor takes in a given functionality or path. These often get grouped so you have a "set" of use cases to account for each scenario.

A Scenario involves a situation that may have single or multiple actors that take a given functionality or path to resolve the scenario.

b) Use case diagrams are used to gather the requirements of a system including internal and external influences. These requirements are mostly design requirements. Hence, when a system is analyzed to gather its functionalities, use cases are prepared and actors are identified.

The purpose of use case diagram is to capture the dynamic aspect of a system. However, this definition is too generic to describe the purpose, as other four diagrams (activity, sequence, collaboration, and State chart) also have the same purpose.