1. CMPT 275 Software Engineering
Phase: Design
High level design activity

2. Objectives of Design
The design phase takes the results of the requirements analysis phase and evolves these results further
The results of the design phase feeds directly into the implementation phase
Requirements analysis → WHAT the system must do
Next Goal: determine HOW the software system is to accomplish what it must do
Janice Regan, 2008

3. Basis of System Design The design phase uses the analysis model
Non-functional requirements / constraints
Use case model: (from users point of view)
Use cases and use case diagrams
state diagrams
Object model:
Context diagram, class diagrams
Janice Regan, 2008

4. Objectives of System Design
The design phase produces a system model
That is based on specific design goals for the designers
That defines architecture and Subsystem design
Identifying subsystems/modules (manageable parts)
Identifying architecture (hardware/software)
Data management / mapping
Access control, flow control (sequencing operations)
That describes boundary use cases:
Initialization, termination, configuration, exception handling
Janice Regan, 2008

5. System design activities
Functional requirements
Non Functional requirements
Analysis
Analysis dynamic model
Analysis object model
System design
Design goals
Subsystem decomposition
Object design
Janice Regan, 2008

6. Objectives of system design
Transforms analysis model (from requirements analysis) into a system design model
Identify, model system architecture
Develop an efficient system decomposition
Identify boundary use cases describing configuration, startup, shutdown, exceptional conditions.
Janice Regan, 2008

7. Design goals, System decomposition
Identify design goals (choose aspects of the system to be optimized) Design goals are often derived from non-functional requirements.
Guide designers in assessing trade offs
Develop and refine a subsystem decomposition that satisfies the maximum number of design goals and or the most critical design goals
Refine the decomposition to better satisfy the design goals
Janice Regan, 2008

8. Design goals When assessing design goals consider
Selection of existing components (off the shelf modules or components )
Hardware / software mapping,
Are there multiple nodes or systems
What is each node responsible for
selecting solutions for managing persistent data
Access control policies
Control flow on a solution wide basis
Boundary conditions (startup, error, shutdown)
Janice Regan, 2008

9. Map of design phase DESIGN LOW LEVEL (object) DESIGN HIGH LEVEL
(system)DESIGN
Data
Persistence
Subsystem
Classes
Class Interfaces
Interaction Diagrams
Module Interfaces
Modularization
architecture
User Interface
User Manual
Implementation
Janice Regan, 2008

10. Why a User Interface Module?
Making the GUI a module
Easy replacement/expansion of interface
Can easily replace without changing functionality of the system ( What if you wanted a command line interface, or a modified version of the GUI)
Janice Regan, 2008

11. User Interfaces Facilitate two-way communication with user
It is a good idea to keep the user interface and the functionality of software system separate
Functionality of software system determines what information is to be communicated (content) and user interface determines how that information is to be communicated (form)
Janice Regan, 2008

12. Guidelines for User Interface Design
A user interface should:
Be simple
Speak the user’s language
Maximize user’s prior knowledge & minimize memorization
Be intuitive
Be consistent
Provide feedback
Give control to the user
Prevent errors
Accommodate multiple skill levels
Janice Regan, 2008

13. Guidelines for UI Design
Be simple
Reduce clutter, make UI transparent
Minimize number of mouse clicks / keyboard characters, levels of navigation
Maximize user’s prior knowledge & minimize memorization
Use interfaces similar to those a user will be familiar with from other applications on his/her platform
Janice Regan, 2008

14. Guidelines for UI Design
Speak the user’s language
Use terms from the users application domain where appropriate
Be intuitive
Combine logically related options
Use meaningful labels, names, icons
Janice Regan, 2008

15. Guidelines for UI Design
Be consistent
Don’t make a labeled button do different things in different places
Use the same approaches throughout
Accommodate multiple skill levels
Have multiple ways to complete a task (e.g. mouse click or keyboard shortcut)
Janice Regan, 2008

16. Guidelines for UI Design
Provide feedback
Clear error messages. Include instructions on how to recover from the problem
Explain what acceptable input is and if necessary why it is acceptable
Indicate when the system is busy, the user should know if the system is working or has crashed (stopped)
Context sensitive help
Janice Regan, 2008

17. Guidelines for UI Design
Give control to the user
Allow the user to undo, redo, confirm, cancel, exit … as appropriate
Warn the user if an operation cannot be undone
Prevent errors
Anticipate and disallow user actions that could lead to errors
Janice Regan, 2008

18. What’s the Problem?
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19. What’s the Problem?
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20. What’s the Problem?
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21. What’s the Problem?
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22. What’s the Problem?
The company claims this was just a joke and never meant to be seen by users. The programmer who did it no longer works for the company, and many thousands of letters of apology were sent to customers.
Janice Regan, 2008

23. What’s the Problem?
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24. What’s the Problem?
Outlook actually has found the Calendar folder, it just lacks permission to read it.
Janice Regan, 2008

25. What’s the Problem?
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26. What’s the Problem?
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27. What’s the Problem?
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28. What’s the Problem?
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29. What’s the Problem?
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30. What is the problem?
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31. What is the problem?
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32. What is the problem?
This window appears when you attempt to disconnect the secure file transmission tool during an file transfer
Janice Regan, 2008

33. What’s the Problem?
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34. What’s the Problem?
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35. What’s the Problem?
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36. User Interface Design
The User interface is how your user interacts with your program
Specifying which actions it should perform
Evaluating, viewing, and saving results
It should not be tied to how your program determines the results
When designing your interface think in terms of how the user will see the system, make the system easy for the user (not the designer) to use and understand.
Janice Regan, 2008

37. User-Centered Design
1. Analyse: who are the users, how are tasks currently performed, steps presently taken while doing task, how user knows if task was successful …
2. Design: draft your user interfaces using…
UI descriptions from your SRS
Guidelines for User Interface Design
Janice Regan, 2008

38. User-Centered Design
3. Evaluate: Run your user interfaces by the users
Do users know what to do at each step
Do users know how to accomplish each step
4. Iterate: Goto step 1.
Our goal -> User satisfaction,
To the user the interface is the system
Janice Regan, 2008

39. Users view of a system
The users view of a system is the UI. The user does not know or need to know or care how the internals of the system functions.
The users understanding of the system is based on their interaction with the UI and their knowledge of the application area
Requirements analysis defines what the system does and collects information about how those tasks are normally done in the application area.
Incorporate how it is done in the design of your UI.
Janice Regan, 2008

40. UI Descriptions
Describe the interaction between software system and actors
Start with UI descriptions and use cases in requirements (remember these should contain only enough detail to be able to explain the behavior of the system)
Refine use cases, add the ‘how’ to the UI descriptions
Janice Regan, 2008

41. UI Descriptions Guideline: 1 interface per actor
Each actor has their own initial screen
That screen may lead to a series of screens performing all required tasks
Later screen in the sequence may be common to multiple actors
Janice Regan, 2008

42. User Interface Design: Project
For requirements analysis UI screens were functional
focused on purpose of screen, not its layout
In Design, focus on screen layout.
Many functions may be incorporated into one window. Multiple screens from requirements may be merged for simplicity
Consider various types of widgets, select the best for each purpose (simplest?)
Janice Regan, 2008