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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 usability
• Have users work with and give their feedback about prototypes, on-line help and draft user manuals

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 Basics of User Interface Design

• User interface design should be done in conjunction with other software engineering activities.
• Do use case analysis to help define the tasks that the UI must help the user perform.
• Do iterative UI prototyping to address the use cases.
• Results of prototyping will enable you to finalize the requirements.

Aspects of usability

Usability can be divided into separate aspects:

• Learnability —The speed with which a new user can become proficient with the system.
• Efficiency of use —How fast an expert user can do their work.
• Error handling —The extent to which it prevents the user from making errors, detects errors, and helps to correct errors.
• Acceptability. —The extent to which users like the system.

Different learning curves

7.4 Usability Principles

1. Do not rely only on usability guidelines – always test with users****. - Usability guidelines have exceptions; you can only be confident that a UI is good if you test it successfully with users. 2: Base UI designs on users’ tasks****. - Perform use case analysis to structure the UI. 3: Ensure that the sequences of actions to achieve a task are as simple as possible. - Reduce the amount of reading and manipulation the user has to do. - Ensure the user does not have to navigate anywhere to do subsequent steps of a task.

Usability Principles

4: Ensure that the user always knows what he or she can and should do next.

• Ensure that the user can see what commands are available and are not available.
• Make the most important commands stand out. 5: Provide good feedback including effective error messages.
• Inform users of the progress of operations and of their location as they navigate.
• When something goes wrong explain the situation in adequate detail and help the user to resolve the problem.

Usability Principles

8: Use understandable encoding techniques****.

• Choose encoding techniques with care.
• Use labels to ensure all encoding techniques are fully understood by users. 9: Ensure that the UI’s appearance is uncluttered****.
• Avoid displaying too much information.
• Organize the information effectively.

Usability Principles

10: Consider the needs of different groups of users.

• Accommodate people from different locales and people with disabilities.
• Ensure that the system is usable by both beginners and experts. 11: Provide all necessary help****.
• Organize help well.
• Integrate help with the application.
• Ensure that the help is accurate.

Some encoding techniques

• Text and fonts
• Icons
• Photographs
• Diagrams and abstract graphics
• Colours
• Grouping and bordering
• Spoken words
• Music
• Other sounds
• Animations and video
• Flashing

Example

(bad UI)

7.5 Evaluating User Interfaces

Heuristic evaluation

1. Pick some use cases to evaluate.
2. For each window, page or dialog that appears during the execution of the use case —Study it in detail to look for possible usability defects.
3. When you discover a usability defect write down the following information: —A short description of the defect. —Your ideas for how the defect might be fixed.

Evaluating User Interfaces

Evaluation by observation of users

• Select users corresponding to each of the most important actors
• Select the most important use cases
• Write sufficient instructions about each of the scenarios
• Arrange evaluation sessions with users
• Explain the purpose of the evaluation
• Preferably videotape each session
• Converse with the users as they are performing the tasks
• When the users finish all the tasks, de-brief them
• Take note of any difficulties experienced by the users
• Formulate recommended changes