Practical Software Engineering

Human Factors

• Design Guidelines
• Graphical User Interfaces
• Direct manipulation
• Desktop metaphor
• Menu systems
• Command interfaces
• Error message design
• Xerox Star
• Principles of the Star User Interface
• User Interface Management Systems
• Neuron Data Open Interface

Design Guidelines

• Use the user's model
• Seeing and pointing vs. remembering and typing
• Avoid acausality
• Provide feedback
• Uniformity and consistency
• Reset and undo
• Provide shortcuts for the power user
• Provide informative error messages
• Make the system crash proof
• Base manuals/tutorials on user interaction
• Users don't read manuals

Graphical User Interfaces

These have:

• Multiple windows including different applications
• Icons for files, folders, applications
• Command selection via menus or keyboard
• Pointing device, usually a mouse
• Graphical and text display

• Easy to learn and use
• Switching applications is easy
• Full screen interaction supported

• complex
• need graphical display
• allocation of control (program or user) difficult

Direct manipulation (e.g. mouse)

• novices can learn basic functionality quickly
• experts can work extremely rapidly
• casual users can retain operational concepts
• error messages are rarely needed
• users can see if they are doing what they thought
• reversibility available (usually)
• users have reduced anxiety

• model specificity
• may limit attention to physical constraints
• repetitive operations are tedious
• may not conform to user expectations
• precision in manipulating objects required

Desktop metaphor

• well-determined for a wide spread of users
• creates enthusiasm
• minimum of training required
• creates concrete images of objects and functions

• needs graphical display
• complex and difficult to design
• concrete metaphors may not be applicable to all office tasks
• extension of metaphor may conflict with user's model
• continually switching between mouse and keyboard

Menu systems

• requires only a standard screen
• restricted keyboard or mouse can be used
• actions allowed need not be remembered
• no typing required
• little user training required
• pop-up and pull-down save screen space

• overdetermined or inflexible
• only a few items can be displayed
• frustrating to experienced users
• discourages typing ahead
• problems negotiating large hierarchies
  • uncertainty about content of a category
  • retrieval will fail if item not there
  • confusion and disorientation in large system
  • difficulty in recalling path causes erratic searches

• Scrolling menus
• Walking menus
• Hierarchical menus

Command interfaces (prompt-response)

• simple
• terse -- little typing
• feedback of dialog state
• commonality between interface and previous experience
• popular with computer experts
• immediacy of response
• allows parallel events to occur in dialog

• minimal feedback on system state
• encourages a mixture of interfaces from different applications
• impossible to refer to previously displayed information
• very underdetermined or overly secretive

Error message design

Messages should be:

• Polite
• Positive
• Concise
• Consistent
• Constructive

They should:

• Suggest how the error could be corrected
• Allow editing or re-entry
• Provide context information
• Offer context help

Xerox Star

Based on a physical office or desktop metaphor.

It is a multifunctional system combining document creation, data processing, electronic filing, mailing, and printing.

It adheres to a small set of design principles which make it seem familiar and friendly, simplify the HCI, unify its functions and allow transfer of experience.

Aim is to minimize modes of interaction, e.g.:

• E(verything)--select whole document
• D(elete)--delete it
• I(nsert)--enter insert mode
• T--type a "T"

Star has:

• Mouse
• Windows
• Document creation -- text editing, page layout, graphics editing, mathematical formula editing
• Data processing -- relational database
• Electronic filing -- Ethernet LAN
• Electronic mail -- communication among workstations
• Printing -- laser printer for hard copy
• Data icons -- documents, folders, record files -- objects on which actions are performed.
• Function icons -- file drawers, floppy disks, calculators, printers -- objects which perform actions.
• Property sheets associated with objects e.g. icons -- alternate representation to icon display, only properties relevant to the object are displayed
• Option sheets associated with commands -- displays arguments to a command, lets you execute the command
• Command classes:
• Editing -- conventional editing, conceptual editing (e.g. desktop)
• Information retrieval -- traditional database, extensions to notion of database (e.g. file drawers of documents, in-baskets of mail)
• Copying -- creation by copying.
• Universal commands:
• move
• copy
• delete
• again
• show properties
• copy properties
• undo
• help

Principles of the Star User Interface

• Familiar user's conceptual model
  • desktop metaphor -- electronic counterparts of physical objects made users more comfortable and cut down training needed.
• Seeing and pointing vs remembering and typing
  • Star displays commands and features to the user. Desktop functions are displayed as icons, property/option sheets define available options.
• What you see is what you get
  • Star gives accurate view of what user does. No conversion needed for text documents.
• Universal commands
  • Star commands used throughout system e.g. COPY can be used in the same way on a word, line or paragraph.
• Consistency
  • Mechanisms are used in the same way wherever they occur. This is achieved through the setting up of strict paradigms and aided by the use of classes and subclasses. (Some minimal contradiction does occur.)
• Simplicity
  • Trade-offs between easy novice use and efficient expert use were made. Common functions were made simple at the expense of uncommon ones being more difficult.
• Modeless interaction
  • Modes are not desirable -- can lead to unexpected results. (Few areas where modes are implemented.) When a mode is accessed, it is made clear to the user.
• User tailorability
  • Star has many provisions for extensibility built in so users can speed up often-performed operations.

User Interface Management Systems

• A special category of CASE tools.
• First designed as tools that allow a user to program a personalized interface:
• Organize and design screen layouts
• Interactively create layout, icons, menus, help screens
• Now usually used by software developers as:
• User has to be quite knowledgeable
• User must have programming experience

Some UIMS allow porting to other platforms e.g. Open Interface, XVT.

Neuron Data Open Interface

• Designed to radically change the economics of developing applications with GUIs for any standard windowing system.
• Multi-standard, multi-platform GUI development environment.
• Comprises a set of ANSI C libraries and an interface layout tool with which developers can build GUIs which are portable across all major windowing, operating system and hardware standards.
• These include
  • OSF/Motif,
  • OPEN LOOK,
  • OS/2 Presentation Manager,
  • Microsoft Windows 3.0,
  • Macintosh.
• Superset used of widgets available in all native toolkits, and extensible to new widgets not offered in any toolkit.
• Open Editor is used to layout components of an applications's GUI using point-and-click.
• Generates resource files, C templates, makefiles.
• Developer must customize C templates to add interface logic and back-end functionality.
• Makefile is used to compile code and link to Open Interface libraries.
• To port to another platform the resource and C source code files are transferred, then recompiled and relinked with Open Interface libraries for that platform.