CSE3308/CSC3080 - Software Engineering: Analysis and DesignLecture 6A.1 Software Engineering:...

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


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


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


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


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


The interaction between the three models

System

Designer User

ImplementationModel

User Model

System Model


Which model should the System Model match?

System Models

Worse Better

ImplementationModel reflects

technology

User Modelreflects user’s

vision


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


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


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


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


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


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


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


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


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


The New Menu’s Appearance

NewOpen...CloseRename/Reposition…Make Snapshot Copy

Make MilestoneRevert to Milestone...

Document Properties...

Abandon Changes

Close

Document


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


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


Design Principles

Affordances

Being aware of the mental models in the

system

Making things visible

The principle of mapping

The principle of feedback


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


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


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


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!


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


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


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?


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


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


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


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



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



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


The Backwards Clock

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93

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