cse3308/csc3080 - software engineering: analysis and designlecture 6a.1 software engineering:...
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CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.1
Software Engineering: Analysis and Design - CSE3308
Conceptual Issues in Human-Computer Interaction
CSE3308/CSC3080/DMS/2000/14
Monash University - School of Computer Science and Software Engineering
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.2
Lecture Outline
CLINTs and WIMPs
What is Human-Computer Interaction?
Models and HCI
An example of the role of models
The need for design
Principles for design
POET - a design method
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.3
CLINTs and WIMPs
CLINT - Command Line INTerfacer WIMPs - Windows, Icons, Mice, Pointing Over the last 4 decades, have migrated from
CLINTs to WIMPs The vast majority of computer users will run
screaming from a command line interface The GUI is now king of our screens, but is
unlikely to stay enthroned forever Voice based systems Virtual Reality based systems
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.4
What is Human-Computer Interaction?
The ways and means by which humans use computers
The interaction between humans and their computers occurs through what is known as the user interface
The User Interface is the “System” If the User Interface is poor, then the system
is poor The User Interface is a necessary but not
sufficient part of building a good system
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.5
Models
People build mental models of how the world works
People form these models through experience, training and instruction
These mental models are often wrong in principle, but correct in effect
In software development, we have three mental models which we are concerned with
The Implementation Model The System Model The User Model
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.6
The interaction between the three models
System
Designer User
ImplementationModel
User Model
System Model
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.7
Which model should the System Model match?
System Models
Worse Better
ImplementationModel reflects
technology
User Modelreflects user’s
vision
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.8
Models and User Interfaces
Mental models are generally simpler than reality
Mental models don’t have to be true or accurate, so long as they are effective
Example - many users see the screen as the centre of the computer where the work is done
Software which has a system model similar to the user’s mental model reduces the complexity of an interface
Most software conforms to the implementation model
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.9
The Baffling Case of the File System
The current file systems used in all systems are based on the implementation model, not the user model
The current file system is an endless source of user problems and frustration
Very few people even question whether it can be done a different way!
Users view files in the same way as they view documents in the real world, but this is not correct
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.10
The real world analogy to using a file
Compare with using a book from a shelf
1. Make a photocopy of the book on the shelf
2. Scribble any changes you want to make on the photocopy
3. Burn the original book on the shelf
4. Place the scribbled on photocopy where the original was
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.11
The current filing system
Differentiates between the copy on the hard disk and the copy in RAM
Use of Hard Disks is purely a technical issue driven by cost, has nothing to do with the usage of the filing system
The ability to lose all your changes and revert to the old version prior to saving is a side-effect and a dangerous side-effect
The existence of two versions of the same document simultaneously is greatly confusing
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.12
A solution in tune with the user’s mental model
What are the goals of a file system for the user?
Saving changes to the document Create a copy of the existing document Naming and renaming the document Placing and repositioning the document Specifying the stored format of the document Creating a milestone copy of the document Reversing some changes Abandoning all changes
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.13
Addressing the requirements
Saving changes to the document With modern technology, we can save often automatically Save when the user stops rather than when actually
typing Manual save facility for the paranoid
Creating a copy of the document Add a command Make Snapshot Copy Give copy standard name like Copy of Alpha and put it in
the same directory Should just happen, no dialog box
Naming and renaming the document Name in the title bar should be editable
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.14
Addressing the requirements (2)
Placing and repositioning the document All documents placed in file system in default location Explicit command on the menu to move to a different
location, if necessary
Specifying the stored format of the document Currently tied in with the file system Not actually part of the file system, but is actually a
property of the document Very rare occurrence, shouldn’t be tied to saving the
document
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.15
Addressing the requirements (3)
Making a Milestone copy of the document creates a version of the document to be stored separately
in the file system similar technology is already used in revision control
systems Simple to revert back to a milestone when we need to
Abandoning all changes a facility on the menu to abandon all changes since the
document was opened with appropriate warnings facility should also be undoable for a week or two
Reversing some changes use a multi-level undo
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.16
The New Menu
Menu now reflects the user’s mental model
instead of the implementation model
there is one document and the user owns it
and can control its behaviour easily and in
detail
No need for the user to worry about copies in
RAM and disk
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.17
The New Menu’s Appearance
NewOpen...CloseRename/Reposition…Make Snapshot Copy
Make MilestoneRevert to Milestone...
Document Properties...
Abandon Changes
Close
Document
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.18
The Need for Design
As can be seen by the File Menu example, there is still room for considerable improvement in user interfaces
By applying good design principles to the tasks that users perform we can produce far better user interfaces
The result is more work for developers, but more productive and better-selling software for users
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.19
Five fallacies
The design is satisfactory for me - therefore it will be satisfactory for everybody
This design is satisfactory for the average person - it will therefore be satisfactory for everybody else
The variability of human beings is so great than it cannot be catered for in any design - but since people are wonderfully adaptable it doesn’t matter anyway
Good interfaces are expensive and since products are usually purchased on appearance and styling, we can ignore interface design
Good interfaces are an excellent idea, I always design things with this in mind, but I do it intuitively and rely on my common sense, so I don’t need to test it
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.20
Design Principles
Affordances
Being aware of the mental models in the
system
Making things visible
The principle of mapping
The principle of feedback
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.21
Affordances
The perceived and actual properties of the thing, primarily those fundamental properties that determine just how the thing could possibly be used
Examples The handle on a door A 3-D pushbutton on a toolbar
Affordances are far more compelling than written instructions
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.22
Making things visible
The functions in a system should be visible Example - the Telephone
standard telephone has 15 function buttons most functions use the * and # button the button has no relationship to the function How many people can set up a three-way call or remember how to
turn off call waiting?
Counter example - the Car Many more buttons, but each button generally has one purpose
and is labelled people have far less problems in a strange car as opposed to
their own telephone
Visibility acts as a reminder of what can be done and how it is done
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.23
The principle of mapping
Mapping is the relationship between two things
for example, the steering wheel of a car, when it is turned right, the car turns right, when turned left, the car turns left
By using natural mappings, the designer can make actions easily learned and always remembered
e.g. spatial analogies: to move an object up, move the control up
e.g. other physical analogies: a louder sound means more, a quieter sound means less
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.24
The principle of feedback
Sending information back to the user on what action has actually been performed and what result has been accomplished
Feedback needs to be timely
Example - Keyboards can easily be made to be silent, but a good keyboard will have a nice satisfying click!
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.25
How people do things An approximate model - Seven Stages of Action Three basic areas
Goals - what does the user want, i.e. their expectations of and intentions for the device?
Execution - how does the user achieve the goals with the device Evaluation - how does the user know whether their goals have been
met?
Gulf of Execution the distance between the intentions of the user and the allowable
actions
Gulf of Evaluation the amount of effort the user must exert to interpret the physical state
of the device and how well it satisfied the user’s intentions and expectations
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.26
The Seven Stages of Action
The World
Goals
Intention to act
Sequence of actions
Execution of theaction sequence
Evaluation ofinterpretations
Interpreting theperception
Perceiving the state of the world
EXECUTION EVALUATION
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.27
Using the seven stages to assess a design
Determine the function of the device?
How easily can one:
Tell what actions are possible?
Determine mapping from intentionto physical movement?
Perform the Action?
Tell of the system is inthe desired state?
Determine mapping from systemstate to interpretation?
Tell what state the system is in?
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.28
POET - a design method
The Psychology of Everyday Things - Donald Norman - Apple Fellow
Address the goals of the user Use both knowledge in the head and knowledge in the
world Simplify the structure of tasks Make things visible, bridge the gulfs of Execution and
Evaluation Get the mappings right Exploit the power of constraints, both natural and
artificial Design for error When all else fails, standardise
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.29
POET - A design method (2) Address the goals of the user
Don’t allow the implementation model to rule the way things are done
Use knowledge in the head and knowledge in the world
People learn better and feel more comfortable when the knowledge needed to do the job is available externally
But knowledge in the world must have a natural, easily interpreted relationship between that knowledge and the information it is intended to convey about possible actions and outcomes
Knowledge in the head improves performance, so the design should not impede experienced users with that knowledge
Knowledge in the head is only available within a context
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.30
POET - a design method (3)
Simplify the structure of the tasks; 4 ways: Keep the task much the same but provide mental aids
» e.g. providing a drop-down list box of postcodes Use technology to make things visible and reduce
memory load
» the automatic spelling check function in Word 97 Remove some parts of the task with automation
» e.g. filling in the suburb field based on the postcode Change the nature of the task
» e.g have a web page and let the user fill in the details
Simplify, but don’t take control away from the user
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.31
POET - a design method (4) Make things visible Bridge the Gulf of Execution by
letting people know what is possible letting people know how actions are performed
Bridge the Gulf of Evaluation by showing people the effects of their actions
Actions should match intentions and expectations The system state should be readily perceivable
and interpretable The system state should match the user’s
intentions and expectations
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.32
POET - a design method (5)
Get the mappings right between intentions and possible actions between actions and their possible effects on the system between actual system state and what the user can
perceive between the perceived system state and the needs,
intentions and expectations of the system
Exploit the power of constraints use constraints so that the user feels there is only one
choice:
» the right one reduce the possible number of actions at any stage
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.33
POET - a design method (6)
Design for error Assume any error can be made and plan for it Support, don’t fight the user’s response Allow recovery from errors Don’t straitjacket the user:
» what you think is an error may be normal behaviour in the system
When all else fails, standardise If there must be arbitrary mappings, standardise the
layout Standards are hard to agree upon Users must be trained in standards
CSE3308/CSC3080 - Software Engineering: Analysis and Design Lecture 6A.34
The Backwards Clock
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