One of the nine diagrams of UML’s are the Use-case Diagram. These are not only important but necessary requirement for software projects. It is basically used in Software life cycles. As we know there are various phases in the development cycle and the most used phase for Use-cases would be during the requirements gathering phase.
A use-case describes a sequence of actions, performed by a system that provides value to an actor. The use-case describes the system’s behavior under various conditions as it responds to a request from one of the stakeholders, called the primary actor.
The actor is the Who of the system, in other words he the end user.
In software and systems engineering, a use-case is a list of steps, typically defining interactions between a role (known in UML as an "actor") and a system, to achieve a goal. The actor can be a human or an external system.
A use-case specifies the flow of events in the system. It is more concerned with what is performed by the system in order to perform the sequence of actions.
A use-case provides the following benefits −
It is an easy means of capturing the functional requirement with a focus on value added to the user.
Use-cases are relatively easy to write and read compared to the traditional requirement methods.
Use-cases force developers to think from the end user perspective.
Use-case engage the user in the requirement process.
Name : Descriptive name that illustrates the purpose of the use-case.
Description : Describes what the use-case does in couple of sentences.
Actor : List any actors that participate in the use-case.
Pre-condition : Conditions that must be met prior to starting the use-case.
Flow of events : Description of interaction between the system and the actor.
Post Condition : Describe the state of the system after a use-case has run its course.
Document each use-case using the template given in the end of this chapter. This section provides a description of each section in the use-case template.
Use-Case ID − Give each use-case a unique numeric identifier, in hierarchical form: X.Y. Related use-cases can be grouped in the hierarchy. Functional requirements can be traced back to a labelled use-case.
Use-Case Name − State a concise, results-oriented name for the use-case. These reflect the tasks the user needs to be able to accomplish using the system. Include an action verb and a noun. Some examples −
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Here, we mention about the names of the people who are the stakeholders of the Usecase document.
Created By − Supply the name of the person who initially documented this usecase.
Date Created − Enter the date on which the use-case was initially documented.
Last Updated By − Supply the name of the person who performed the most recent update to the use-case description.
Date Last Updated − Enter the date on which the use-case was most recently updated.
The following are the definitions of the key concepts of Use-Case −
An actor is a person or other entity external to the software system being specified who interacts with the system and performs use-cases to accomplish tasks. Different actors often correspond to different user classes, or roles, identified from the customer community that will use the product. Name the actor(s) that will be performing this usecase.
Provide a brief description of the reason for and outcome of this use-case, or a high-level description of the sequence of actions and the outcome of executing the use-case.
List any activities that must take place, or any conditions that must be true, before the use-case can be started. Number each precondition.
Describe the state of the system at the conclusion of the use-case execution. Number each post condition.
Indicate the relative priority of implementing the functionality required to allow this usecase to be executed. The priority scheme used must be the same as that used in the software requirements specification.
Estimate the number of times this use-case will be performed by the actors per some appropriate unit of time.
Provide a detailed description of the user actions and system responses that will take place during execution of the use-case under normal, expected conditions. This dialog sequence will ultimately lead to accomplishing the goal stated in the use-case name and description. This description may be written as an answer to the hypothetical question, “How do I <accomplish the task stated in the use-case name>?” This is best done as a numbered list of actions performed by the actor, alternating with responses provided by the system.
Document other, legitimate usage scenarios that can take place within this use-case separately in this section. State the alternative course, and describe any differences in the sequence of steps that take place. Number each alternative course using the Use-case ID as a prefix, followed by “AC” to indicate “Alternative Course”. Example: X.Y.AC.1.
Describe any anticipated error conditions that could occur during execution of the usecase, and define how the system is to respond to those conditions. Also, describe how the system is to respond if the use-case execution fails for some unanticipated reason. Number each exception using the Use-case ID as a prefix, followed by “EX” to indicate “Exception”. Example: X.Y.EX.1.
List any other use-cases that are included (“called”) by this use-case. Common functionality that appears in multiple use-cases can be split out into a separate use-case that is included by the ones that need that common functionality.
Identify any additional requirements, such as nonfunctional requirements, for the usecase that may need to be addressed during design or implementation. These may include performance requirements or other quality attributes.
List any assumptions that were made in the analysis that led to accepting this use-case into the product description and writing the use-case description.
List any additional comments about this use-case or any remaining open issues or TBDs (To Be Determined) that must be resolved. Identify who will resolve each issue, the due date, and what the resolution ultimately is.
Version control is the management of changes to documents, large websites, and other collection of information. Changes are usually identified by a number or letter code, termed as revision number or revision level. Each revision is associated with a timestamp and person making the change.
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