use case diagram

Information about use case diagram

Published on March 6, 2011

Author: Saurabh6



Use Case Diagrams : Use Case Diagrams BCA Sem IV K.I.R.A.S The Use Case Diagram : Overview: The Use Case Diagram : Overview The use case diagram is the first that designers will work with when starting a project.  This diagram allows for the specification of high level user goals that the system must carry out A use case diagram is an excellent way to communicate to management, customers, and other non-development people what a system will do when it is completed. Saurabh The Use Case Diagram : Overview: The Use Case Diagram : Overview More formally, a use case is made up of a set of scenarios.  Each scenario is a sequence of steps that encompasses of an interaction between a user and the system.  The use case brings scenarios together that accomplish a specific goal of the user. A use case can be specified by textually describing the steps required and any alternative actions at each step.  Use Case diagrams show the various activities the users can perform on the system. They model the dynamic aspects of the system. Provides a user’s perspective of the system. Use case diagrams consist of named pieces of functionality (use cases), the persons or things invoking the functionality (actors), and possibly the elements responsible for implementing the use cases Saurabh The Use Case Diagram : Overview: The Use Case Diagram : Overview With the help of a use case diagram, you can discuss and communicate: The scenarios in which your system or application interacts with people, organizations, or external systems. The goals that it helps those actors achieve. The scope of your system. Saurabh The Use Case Diagram : Purpose: The Use Case Diagram : Purpose The main purpose of a use case diagram is to show who interacts with your system, and the main goals they achieve with it. Its purpose is to present a graphical overview of the functionality provided by a system in terms of actors, their goals (represented as use cases), and any dependencies between those use cases. Documents the functionality of the system from the users perspective. Also to document the interaction between the users and the system using supporting use case descriptions. Use case diagrams are used to show the behavior of the system we are developing. Saurabh Elements of a Use Case Diagram: Elements of a Use Case Diagram Actors: Use case: System boundary: Associations Relationships Saurabh Use Case Diagrams - Actors: Use Case Diagrams - Actors An actor is a user of the system playing a particular role.  Examples of actors are salesperson, manager, support person, and web store system. An actor in a use case diagram interacts with a use case . For example, for modeling a banking application, a customer entity represents an actor in the application. Similarly, the person who provides service at the counter is also an actor. When creating a use case model, we are not concerned with the individuals, only the roles that they play. A user is external to the system To identify an actor, search in the problem statement for business terms that portray roles in the system. For example, in the statement "patients visit the doctor in the clinic for medical tests," "doctor" and "patients" are the business roles and can be easily identified as actors in the system. Actor is shown with a stick figure. employee Saurabh Use Cases: Use Cases Use case is a particular activity a user can do on the system. Is represented by an ellipse. Uses of Use Cases Helps capture system requirements Useful for validating the system Use Cases Documentation A single use case represents a task that is required of the system Include a text description of each use case A use case diagram is a concise summary of the text descriptions Following are two use cases for a library system. Borrow Reserve Saurabh System boundary: System boundary A system boundary defines the scope of what a system will be. A system cannot have infinite functionality. So, it follows that use cases also need to have definitive limits defined. A system boundary of a use case diagram defines the limits of the system. The system boundary is shown as a rectangle spanning all the use cases in the system. The system boundary is potentially the entire system as defined in the problem statement Saurabh Associations: Associations On a use case diagram, associations are drawn between actors and use cases to show that an actor carries out a use case.  A use case can be carried out by many actors and an actor may carry out many use cases. In the diagram, the actors are shown as the stick figure shapes on the left, the use cases are the ellipses, and the associations between them are represented by the connecting lines LOGIN Client Saurabh Relationships: Relationships Use cases can also be related to each other with three different links. Inclusion Inclusion enables to reuse one use case's steps inside another use case. In general, the includes link is to avoid repetition of scenarios in multiple use cases . use cases that are included as parts of other use cases Extension Allows creating a new use case by adding steps to existing use cases. U se cases that extend the behavior of other core use cases. Generalization Allows child use cases to inherit behavior from parent use cases Saurabh Include: Include When a use case is depicted as using the functionality of another use case in a diagram, this relationship between the use cases is named as an include relationship. Literally speaking, in an include relationship, a use case includes the functionality described in another use case. An include relationship is depicted with a directed arrow having a dotted shaft. For example, in Figure, you can see that the functionality defined by the "Validate patient records" use case is contained within the "Make appointment" use case. Hence, whenever the "Make appointment" use case executes, "Validate patient records" use case is also executed. Saurabh Extend:: Extend: In an extend relationship between two use cases, the child use case adds to the existing functionality and characteristics of the parent use case. An extend relationship is depicted with a directed arrow having a dotted shaft, similar to the include relationship. The tip of the arrowhead points to the parent use case and the child use case is connected at the base of the arrow. Figure shows an example of an extend relationship between the "Perform medical tests" (parent) and "Perform Pathological Tests" (child) use cases. The "Perform Pathological Tests" use case enhances the functionality of the "Perform medical tests" use case. Saurabh Example of extends: Example of extends Saurabh Example of Include: Example of Include The figure shows a Use Case Diagram for an on-line CD catalog.  The system has a single actor: the on-line customer.  The customer can browse the catalog, search for a CD, add a CD to the order, view the order details, and place the order. Both "View Order Details" and "Place Order" use "Calculate Order Total". Saurabh Use Case Diagram for Student Assessment Management System: Use Case Diagram for Student Assessment Management System The actors are Teacher, Student, Printing Administrator The use cases are Record grades, View grades, distribute report cards, create report cards Association Teacher Student Printing administrator Grade system Record grades View grades Distribute Report cards Create report cards System boundary Saurabh Examples: Examples Reservation System Bookshop Mgmt. Saurabh Inheritance Between Actors: Inheritance Between Actors The potential reuse within use-case models occurs between actors: an actor on a use-case diagram can inherit from another actor. the “International Student” actor inherits from “Student.” An international student is a student, the only difference being is he or she is subject to different rules and policies (the international student pays more in tuition and is restricted from taking several seminars). Saurabh Inheritance Between Actors: Inheritance Between Actors Example : The specialized actor, such as Club Customer in the example, inherits the use cases of the generalized actor, such as Customer. The arrowhead should point at the more general actor, such as Customer. The specialized actor can have its own additional use cases that are not available to the other actors Make Payment Choose Seat customer Club customer Saurabh

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