While developing the information system, it is necessary to verify that correct and necessary requirements for the system are included in the system. There are various models that can be used to verify and validate the requirements in the system. The most important issue that information technology community face during the development of the system is to specify the requirements of the user. The functional requirements of users are necessary for the system to be verified. In this case, the information technology used the traditional ways to express the requirements specification to the user by using data flow diagrams or entity relationship diagrams. These types of modes are not understandable to the non-technical users.
In order to provide the specification for the requirements in the system, a list of requirements is maintained in the term of the system shall perform. In most of the cases, the requirements in the list are either conflict or duplication requirements are specified. In this matter, it is not easy to compile and specify all the requirements of the system in a better manner.
Another method which is traditionally adopted to describe the functionality of the system is functional decomposition. As its name suggests, in this method the major tasks of the system are divided into semi-functions or sub-processes. The sub-processes become the programs in this method which are easy to maintain. The disadvantage of this method is that it is linked to COBOL and mainframes, which means it cannot be used for an application that is web-based or object-oriented.
In order to overcome all these problems, the use-case modelling is considered as one of the best ways for requirement specification. With the help of use-case model of the information system, it is easy for the users to understand the working of the system and can verify and validate the requirements of the system.
Use Case Diagram
The use case diagram is also considered as behaviour diagram through which the functions of the system are specified by describing the actions that will be performed by the users in the system. The users who perform actions in the system are known as actors and functions of the system are known as the action of the system. The use case diagram includes the diagrams and texts that represent the processes and functionality of the system among various actors who are included in it.
The use case diagram example for the student management system is as follows:
There six graphics elements that are used to prepare the user interface diagram for the information system. Such elements are:
- Use Cases
There are basically two types of requirements that are considered while developing the use case diagram of information systems such as functional requirement and non-functional requirement.
Functional Requirement: The functional requirement is those actions that the system must be performed without taking any physical consideration from the user. Taking the input from the user and providing the results as output to the user is considered as the functional requirement of the user. The functional requirements specify the input and output of the system that will be accepted and must be provided by the system.
Non-functional requirements: The non-functional requirements of the system are those in which direct functions of the system are not considered. The non-functional requirements are the qualities of the system that the system must have such as scalability, reliability, performance and supportability of the system.
Basic concepts of Use Case modelling
A use case of information system generally describes the sequences of actions that are performed actors including variant sequences and error sequences which can be performed by the system. The Use case in most cases is presented in the form of text or high-level graphical view to represent the actions and processes of the system.
In UML 2.0, the system boundary is the subject in the use case modelling which defines that what or who can use the system and perform the actions it the system and what kind of response that system will provide to actors against their actions. The actors in the use case represent the role of those external entities that perform different actions in the system. The use case diagram helps the users to identify the use cases which are specified in the textual form.