《面向对象软件工程》课程PPT教学课件（英文版）Chapter 7：Focusing on Users and Their Tasks

object-Oriented Software Engineering Practical Software development using uml and Java Chapter 7 Focusing on Users and their Tasks www.oseng.com

Object-Oriented Software Engineering Practical Software Development using UML and Java Chapter 7: Focusing on Users and Their Tasks

7.1 User Centred design Software development should focus on the needs of users Understand your users Design software based on an understanding of the users tasks Ensure users are involved in decision making processes Design the user interface following guidelines for good usabilit Have users work with and give their feedback about prototypes, on-line help and draft user manuals www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 2 7.1 User Centred Design Software development should focus on the needs of users • Understand your users • Design software based on an understanding of the users’ tasks • Ensure users are involved in decision making processes • Design the user interface following guidelines for good usability • Have users work with and give their feedback about prototypes, on-line help and draft user manuals

The importance of focusing on users Reduced training and support costs Reduced time to learn the system Greater efficiency of use Reduced costs by only developing features that are needed Reduced costs associated with changing the system later Better prioritizing of work for iterative development Greater attractiveness of the system, so users will be more willing to buy and use www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 3 The importance of focusing on users • Reduced training and support costs • Reduced time to learn the system • Greater efficiency of use • Reduced costs by only developing features that are needed • Reduced costs associated with changing the system later • Better prioritizing of work for iterative development • Greater attractiveness of the system, so users will be more willing to buy and use it

7.2 Characteristics of users Software engineers must develop an understanding of the users Goals for using the system Potential patterns of use Demographics Knowledge of the domain and of computers Physical ability Psychological traits and emotional feelings www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks 4

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 4 7.2 Characteristics of Users Software engineers must develop an understanding of the users • Goals for using the system • Potential patterns of use • Demographics • Knowledge of the domain and of computers • Physical ability • Psychological traits and emotional feelings

7.3 Developing use-Case Models of Systems a use case is a typical sequence of actions that a user performs in order to complete a given task The objective of use case analysis is to model the System from the point of view of how users interact with this system when trying to achieve their objectives a use case model consists of - a set of use cases an optional description or diagram indicating how they are related www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 5 7.3 Developing Use-Case Models of Systems A use case is a typical sequence of actions that a user performs in order to complete a given task • The objective of use case analysis is to model the system … from the point of view of how users interact with this system … when trying to achieve their objectives. • A use case model consists of — a set of use cases — an optional description or diagram indicating how they are related

Use cases In general, a use case should cover the full sequence of' steps from the beginning of a task until the end a use case should describe the user 's interaction with the system -not the computations the system performs a use case should be written so as to be as independent as possible from any particular user interface design a use case should only include actions in which the actor interacts with the computer www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks 6

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 6 Use cases • In general, a use case should cover the full sequence of steps from the beginning of a task until the end. • A use case should describe the user’s interaction with the system ... —not the computations the system performs. • A use case should be written so as to be as independent as possible from any particular user interface design. • A use case should only include actions in which the actor interacts with the computer

Scenarios a scenario is an instance of a use case It expresses a specific occurrence of the use case -a specific actor at a specific time -with specific data www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 7 Scenarios A scenario is an instance of a use case • It expresses a specific occurrence of the use case —a specific actor ... —at a specific time ... —with specific data

How to describe a single use case A Name: Give a short, descriptive name to the use case B. Actors: List the actors who can perform this use case C. Goals: Explain what the actor or actors are trying to achieve D. Preconditions: State of the system before the use case E. Description: Give a short informal description F. Related use cases G Steps: Describe each step using a 2-column format H. Postconditions: State of the system in following completion www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks 8

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 8 How to describe a single use case A. Name: Give a short, descriptive name to the use case. B. Actors: List the actors who can perform this use case. C. Goals: Explain what the actor or actors are trying to achieve. D. Preconditions: State of the system before the use case. E. Description: Give a short informal description. F. Related use cases. G. Steps: Describe each step using a 2-column format. H. Postconditions: State of the system in following completion

Use case diagrams Register in Course Add Course Offering Registrar Actor Add course Enter Grade for Course Student Find information about cours Professor actor www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 9 Use case diagrams Register in Course Add Course Add Course Offering Student Find information about course Professor Actor Registrar Actor Enter Grade for Course

Extensions Used to make optional interactions explicit or to handle exceptional cases By creating separate use case extensions, the description of the basic use case remains simple a use case extension must list all the steps from the beginning of the use case to the end -including the handling of the unusual situation www.oseng.com O Lethbridge/Laganiere 2001 Chapter 7: Focusing on Users and Their Tasks

© Lethbridge/Laganière 2001 Chapter 7: Focusing on Users and Their Tasks 10 Extensions • Used to make optional interactions explicit or to handle exceptional cases. • By creating separate use case extensions, the description of the basic use case remains simple. • A use case extension must list all the steps from the beginning of the use case to the end. —Including the handling of the unusual situation