CSC/ECE 517 Fall 2007/wiki2 4 2q

From Expertiza_Wiki
Revision as of 20:31, 21 January 2021 by Apkulka2 (talk | contribs)
Jump to navigation Jump to search

A Guide to Use Cases on the WEB

Topic :Use cases. There are even more pages on the Web on use cases than on MVC. If someone wants to learn about them, what should (s)he do? Look at the first few hits in Google? I expect we can do better than that. Write a review of the use-case sites on the Web. Which are best for learning about the concept? Which have the most instructive examples? Which teach advanced concepts that are not apparent in perusing most use-case sites? Read at least several dozen pages before deciding how to organize your overview.

Introduction

This page tries to review the use-case sites on the Web which can be useful to best understand the concept. Also a few instructive examples are covered paying attention to the basic use case as well as advanced concepts that are not apparent in perusing most use-case sites.

What is a Use Case?

Definition

"Use case is a methodology used in software and systems engineering to understand and identify the functional requirements of a system. Use cases describe the interaction between a primary actor, the initiator of the interaction and the system itself, represented as a sequence of simple steps."[1][2]

Simply put, a use case is a description of how a person will interact with the system to achieve a certain goal. It helps to learn if any errors could occur in the process and design features to resolve those errors.

It consists of 3 primary elements:

  • Actor: They are generally the user of the system or an external entity and can be a person or another system itself. A use case can be best described as what happens when the actor is using the system to achieve some goal.
  • System: It describes the process/steps to reach the final outcome.
  • Goal: A goal is an end result which follows the sequence of events as described in the use cases.

Every use case gives a complete list of events which occur from the time the actor starts interacting with the system till the time the final goal is achieved. A use case also records all the possible scenarios that may occur while trying to reach the desired goal. We can think of it as existence of a main course of events that will occur in normal circumstances, to which the exceptional cases are added. Anything that is not relevant to the actor/user is not a part of the use case.

Listed below are a few links to external websites which further illustrate this concept.

UML Diagrams and Use Case Diagrams

"The Use case diagram is used to identify the primary elements and processes that form the system. The primary elements are termed as 'actors' and the processes are called "use cases." The Use case diagram shows which actors interact with each use case."[3]

UML is a collection of diagrams which visually represents a software or a system. A use case diagram is one of its types. They are useful in providing a pictorial view of the interactions between the users (actors) and sets of events (use cases) associated with the system.They also evolve as the projects or system change with time. The standard elements of a use case diagram makes comprehension easy for anyone trying to understand the use case.

Listed below are useful links in understanding how to draw typical use case diagrams.

How to Write a Use Case?

Writing Effective Use Cases

One of the most difficult problem in software development is capturing precisely what you want to build. Inaccurate requirement will end-up with significant delay, rework or even abandonment of the project. Effective applying use case technique helps your team capturing requirements in user point of view which can be easily understood by both the end-user and your team. Use case driven development support subsequent development activities such as analysis and design and testing.

Listed below are useful links in understanding how to write effective use cases.

Examples using Use Cases

In this section, a few instructive examples have been outlined along with their references which illustrate different ways in which use cases can be written. The first example is a basic use-case template.

Basic use case template

Described below are some the characteristics of a typical use case. 

 CHARACTERISTIC INFORMATION
 * Goal in Context:   Buyer issues request directly to our company, expects goods shipped and to be billed.
 * Scope:  Company
 * Preconditions:  We know Buyer, their address, etc.
 * Success End Condition:  Buyer has goods, we have money for the goods.
 * Failed End Condition:  We have not sent the goods, Buyer has not spent the money.
 * Primary Actor:  Buyer, any agent (or computer) acting for the customer
 * Trigger:  purchase request comes in.
 
 MAIN SUCCESS SCENARIO
 1. Buyer calls in with a purchase request.
 2. Company captures buyer’s name, address, requested goods, etc.
 3. Company gives buyer information on goods, prices, delivery dates, etc.
 4. Buyer signs for order.
 5. Company creates order, ships order to buyer.
 6. Company ships invoice to buyer.
 7. Buyers pays invoice.
 
 EXTENSIONS
 3a. Company is out of one of the ordered items: 
     3a1. Renegotiate order.
 4a. Buyer pays directly with credit card:
     4a1. Take payment by credit card (use case 44)
 7a. Buyer returns goods:
     7a. Handle returned goods (use case 105)

The basic steps that can be followed so as to ensure writing an effective use case has been described well in How to Write a use case.[4]

Restaurant

This example provides one use case but distinctly provides a step by step analysis of the events that constitute a use case. It mentions the actors, pre-conditions, exceptions and alternative scenarios.

Purchase order

This example provides a typical use case specification by listing the activity, result, constraints and extensions involved with a purchase order from a Finance web page.

ATM system

This example is a little more involved in that it provides a number of use cases associated with using an ATM system including cash withdrawal, transfers, deposits, balance inquiry, etc.

A shopping website order Process

This is a very good example that describes the scenarios and extensions involved in writing a use case for a online shopping order. It also describes the UML diagram.

Self Service Machine

This example provides typical use cases of a self service machine like supermarket barcode scanners, online banking services, check-in kiosks and so on. Some of the aspects of using a self service machine are: buying a product, re-stocking the machine, collecting the money etc. The following link provides a UML diagram which depicts the interaction between the users and system through the use case of self-service kiosks.

References

External Links

Retrieved from "https://wiki.expertiza.ncsu.edu/index.php?title=CSC/ECE_517_Fall_2007/wiki2_4_2q&oldid=137840"