Saturday, July 15, 2017

Definition of the User View of a System || Object-Oriented Programming

Definition of the User View of a System:

     The user view represents the goals and objects of several of users and their requirements form the system. The user view represents that the system with which the user interacts.

System Users:

     System Users can be human users or other systems that interact directly with the system. The role of a system user is defined based on the functions performed.
      For example, consider the billing system of the department store from where you buy general groceries. The storekeeper who updates the stock details will be the system user.

Actors:

     Actors are the elements that lie outside the system, and therefore are called the external entities of a system. They are used to model system users. Actors interact directly with the system, exchange message and request for some action to be performed.  For example, in the billing system of the department stores, the clerk who enters the product details will be an actor.

   External entities that do not interact directly with the system cannot be termed as actors of the system. For example, in the billing system of the department stores, as a customer, you will not be an actor because you cannot interact with the system directly.
      The actors fall into four main categories:
  1. Principal actors – People who directly interact with the system are called principal actors. In the billing system example, the clerk is the principal actor.
  2. Secondary actors – people who are involved in maintenance of the system are the secondary actors. In the billing system example, the stores in-charge who provides the paper for printing the bill is the secondary actor.
  3. External hardware – The hardware that is a part of system other than the computer that runs an application is called an external hardware. In the billing system example, the printer that is used for printing the bill is external hardware.
  4. Other systems – The external systems with which your system needs to interact for its working are called systems.


Let's clear more by solving the problem: 

    Question: One of the sources used by BMW for recruiting personal is the internal job posting process. Whenever a vacancy arises, the Human Resources (HR) head of the region informs all the employees of that region and also sends the information to the regional HR heads inviting applications. The other regional HR heads then place the vacancy information on the notice board or through the websites. All interested employees send their application with resume to the HR head of the region where the vacancy exists.

Now, identify the various actors interacting with the system? 

Solution:

How to identify Actors:

     To identify actors, you should first identify the context of the system and then understand the environment of the system in which the actors exist.

The Context of a System:
      
      A system addresses a problem and provides solutions to the problem within a framework. This framework is referred to as the context of a system. The context of the problem within the system must be defined and understood first. Then the solution to the problem should be worked out.

     In our problem statement, the context of the system is the HR department where the vacancy exists.

The Environment of a System:
                
     The environment of system specifies the functionality of the system from the user’s point of view. The framework consists of the elements that lie inside the system and are responsible for the working of the system, as well as the elements that lie outside the system and what these elements expect the system to provide.

    In our problem statement, the environment of the system includes the HR heads and employees who lie outside the system. The internal job posting processes lies inside the system.

Who is an actor?

     In our problem statement, the actors would be the HR head of the region where a vacancy arises, the HR heads of other regions and the employees as all these entities interact with system directly.

Who is not an actor?

    External entities that do not interact directly with the system cannot be termed as actors of the system. Some results would be happened for identified:
  1. Regional HR head where a vacancy exists denoted as RHR (V).
  2. Other Regional HR head, denoted as RHR (O).
  3.  All employees of BMW, denoted as EMP.

 Use Cases:
      
      Use cases consist of elements that lie inside the system and are responsible for the working of the system. This is the functionality and behavior of the system. Therefore, use cases are nothing but the actions that the system performs to generate results requested by the actors of the system.

     Use cases represent all the possible events that can occur in all possible scenarios. They represent all interactions that can take place between an actor and the system.

      A relationship represents a logical connection between use cases and actors. Relationship is unidirectional.

    The following are examples of use cases in billing system of a department store:
  1.  Enter Bill Details.
  2. Calculate Total Amount.
  3. Print Bill.

Diagrammatic Conventions for Drawing Use Case Diagrams:

    The user view of a system consists of use case diagrams. A use case diagram contains actors, use cases and their relationship. The diagram describes the behavior of the system, as seen by its end users and developers, as well as their expectations of the system. In short, the use case diagram represents the functionality provided by the system to external entities.

    Use case diagrams consist of actors and use cases. Actors are represented as stick personal and use cases as ellipses. 




Use Case Diagram:


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