Use Case Analysis PDF

Use Case Analysis © Copyright 2011 John Wiley & Sons, Inc. 4-0  Outline Use Cases  Elements of a use case. Alternative use case formats. Use cases and functional requirements. Use cases and testing. Building use cases. © Copyright 2011 John Wi...

Use Case Analysis © Copyright 2011 John Wiley & Sons, Inc. 4-0  Outline Use Cases  Elements of a use case. Alternative use case formats. Use cases and functional requirements. Use cases and testing. Building use cases. © Copyright 2011 John Wiley & Sons, Inc. 4-1  INTRODUCTION  Use cases are a means of expressing user requirements.  Use cases are used extensively in the analysis phase.  A use case represents how a system interacts with its environment by illustrating the activities that are performed by the users and the system’s responses. – Important in Business System Application / Web Sites – more users – Less import: in Batch process, Mathematical , data warehouse  The text-based use case is easy for the users to understand, and also flows easily into the creation of process models and the data model.  Business Scenario = Use Case © Copyright 2011 John Wiley & Sons, Inc. 4-2  USE CASES  A use case depicts a set of activities that produce some output result.  Each use case describes how an external user triggers an event to which the system must respond.  With this type of event-driven modeling, everything in the system can be thought of as a response to some triggering event.  Creation of use cases is often done as a part of interview session with users or a part of JAD sessions. © Copyright 2011 John Wiley & Sons, Inc. 4-3  Example © Copyright 2011 John Wiley & Sons, Inc. 4-4  Elements of a Use Case Basic Information  Each use case has a name and number, and brief description.  The priority may be assigned to indicate the relative significance.  The actor refers to a person, another system, or a hardware device that interacts with the system to achieve a useful goal.  The trigger for the use case – the event that causes the use case to begin. 4-5  Preconditions  It is common practice to create smaller, more focused use cases breaking the whole process down into parts.  It is important to define clearly what needs to be accomplished before each use case begins.  The preconditions define the state the system must be in before the use case commences. 4-6  Normal Course  The next part of a use case is the description of the major steps that are performed to execute the response to the event, the inputs used for the steps, and the outputs produced by the steps.  The normal course lists the steps. 4-7  Alternative Courses Alternative courses depict branches (alternative paths of the steps) in logic that also will lead to a successful conclusion of the use case. 4-8  Postconditions  The postconditions section defines the final product of the use case.  These postconditions also serve to define the preconditions for the next use case in the series. 4-9  Exceptions  A use case should describe any error conditions or exceptions that may occur as the use case steps are performed.  These are not normal branches in decision logic, but are unusual occurrences or errors that could potentially be encountered and will lead to an unsuccessful result. 4-10  Summary of Inputs and Outputs  The final section of the use case summarizes the set of major inputs and outputs of the use case, along with their source or destination. 4-11  Additional Use Case Issues  Additional sections may be included, e.g., - Frequency of use - Business rules - Special requirements - Assumptions - Notes and issues © Copyright 2011 John Wiley & Sons, Inc. 4-12 Chain of use cases – an example © Copyright 2011 John Wiley & Sons, Inc. 4-13  Alternative Use Case Formats  A full-dressed use case is very thorough, detailed, and highly structured. It is valuable when : – Loose coupling between users and developers – Complex process / high risk process – Remote developers/users  The project team may decide that a more casual use case format is acceptable. © Copyright 2011 John Wiley & Sons, Inc. 4-14 Example 4-15 4-16  Analysis involves three steps: – Understand the existing situation (the as-is system) – Identify improvements – Define the requirement for the new system (the to-be system). Requirement elicitation techniques – Interview, JAD , Questionnaire, Document Analysis, Observation Requirement analysis strategies – Problem Analysis, Root cause analysis, Duration Analysis, Activity-based costing, Info Benchmarking Outcome analysis, Tech Analysis, Activity elimination Use case © Copyright 2011 John Wiley & Sons, Inc. 3-17  Use Cases and the Functional Requirements  Use cases are very useful tools to us to understand user requirements. However, use cases only convey the user’s point of view.  Transforming the user’s view into the developer’s view by creating functional requirements is one of the important contributions of system analyst.  The derived functional requirements give more information to the developer about what the system must do. © Copyright 2011 John Wiley & Sons, Inc. 4-18  Exam Question Why Use cases are very useful tools to analyst and whose perspective is given by the use cases ? What is the role of the analyst when develop the requirements of the system using use cases ? © Copyright 2011 John Wiley & Sons, Inc. 4-19 Example 4-20  Use Cases and Testing Building Use Cases  Step 1: Identify the major use cases © Copyright 2011 John Wiley & Sons, Inc. 4-21 Step 2: Identify the major steps for each use case © Copyright 2011 John Wiley & Sons, Inc. 4-22 Step 3: Identify elements within steps © Copyright 2011 John Wiley & Sons, Inc. 4-23 Step 4. Confirm the use case © Copyright 2011 John Wiley & Sons, Inc. 4-24  Exam Question What are the steps of developing uses cases for the system ? © Copyright 2011 John Wiley & Sons, Inc. 4-25 Revise functional requirements based on use cases  The functional requirements in the requirements definition may be modified to reflect the more detailed understanding and to provide insight to the development team on some “back-end” processing. © Copyright 2011 John Wiley & Sons, Inc. 4-26 Example 4-27  SUMMARY  A use case contains all the information needed to build one part of a process model, expressed in an informal, simple way.  When writing a use case, - identify the triggering event, - develop a list of the major steps, - identify the input(s) and output(s) for every step, - have the users role-play the use case to verify. © Copyright 2011 John Wiley & Sons, Inc. 4-28