©ravichandranuser interface slide 1 user interface design

©Ravichandran User interface Slide 1

User interface design


Objectives

To understand what is an User Interface To explain different types of User interface

and its advantages and disadvantages To explain the principal activities in the user

interface design process


Topics covered

Design issues The user interface design process


What is an User Interface

It is a means of communication between the user and the computer


The user interface

User interfaces should be designed to match the skills, experience and expectations of its anticipated users.

System users often judge a system by its interface rather than its functionality.

A poorly designed interface can cause a user to make catastrophic errors.

Poor user interface design is the reason why so many software systems are never used.


Human factors in interface design

Limited short-term memory• People can instantaneously remember about 7 items of

information. If you present more than this, they are more liable to make mistakes.

People make mistakes• When people make mistakes and systems go wrong,

inappropriate alarms and messages can increase stress and hence the likelihood of more mistakes.

People are different• People have a wide range of physical capabilities. Designers

should not just design for their own capabilities. People have different interaction preferences

• Some like pictures, some like text.


UI design principles

UI design must take account of the needs, experience and capabilities of the system users.

Designers should be aware of people’s physical and mental limitations (e.g. limited short-term memory) and should recognise that people make mistakes.

UI design principles underlie interface designs although not all principles are applicable to all designs.


User interface design principles

Principle Description

User familiarity The interface should use terms and concepts which are drawnfrom the experience of the people who will make most use of thesystem.

Consistency The interface should be consistent in that, wherever possible,comparable operations should be activated in the same way.

Minimal surprise Users should never be surprised by the behaviour of a system.

Recoverability The interface should include mechanisms to allow users torecover from errors.

User guidance The interface should provide meaningful feedback when errorsoccur and provide context-sensitive user help facilities.

User diversity The interface should provide appropriate interaction facilities fordifferent types of system user.


Interaction styles

Interaction style

Main advantages Main disadvantages Application examples

GUI Fast and intuitive interaction Easy to learn

May be hard to implement. Only suitable where there is a visual metaphor for tasks and objects.

Video games CAD systems

Menu selection

Avoids user error Little typing required

Slow for experienced users. Can become complex if many menu options.

Most general-purpose systems

Form based Simple data entry Easy to learn Checkable

Takes up a lot of screen space. Causes problems where user options do not match the form fields.

Stock control, Personal loan processing

Command language

Powerful and flexible Hard to learn. Poor error management.Only meant for technical users.

Only Operating systems, Command and control systems

Natural language

Accessible to casual users Easily extended

Requires more typing. Natural language understanding systems are unreliable.

Information retrieval systems


Colour displays

Colour adds an extra dimension to an interface and can help the user understand complex information structures.

Colour can be used to highlight exceptional events.

Common mistakes in the use of colour in interface design include:• The use of colour to communicate meaning;• The over-use of colour in the display.


Colour use guidelines

Limit the number of colours used and be conservative in their use.

Use colour change to show a change in system status.

Use colour coding to support the task that users are trying to perform.

Use colour coding in a thoughtful and consistent way.

Be careful about colour pairings.


Error messages

Error message design is critically important. Poor error messages can mean that a user rejects rather than accepts a system.

Messages should be polite, concise, consistent and constructive.

The background and experience of users should be the determining factor in message design.


User error

Assume that a nurse misspells the name of a patient whose records he is trying to retrieve.

Please type the patient’s name in the box then click on OK

MacDonald, R.

OK Cancel

Patient’s name

In the box and click ok


Good and bad message design

Error #27

Invalid patient id

OK Cancel

System-oriented error messageUser-oriented error message

Name not in listClick on Patients for a list of patientsClick on Retry to re-input the patient’s nameClick on Help for more information

Patients Help Retry Cancel

Bad message design Good message design


The User interface design process

User interface design is an iterative process involving close liaisons between users and designers.

The 3 core activities in this process are:• User analysis. Understand what the users will do with the

system;• System prototyping. Develop a series of prototypes for

experiment;• Interface evaluation. Experiment with these prototypes

with users before the final user interface is framed.


The design process

Executableprototype

Designprototype

Produce paper-based design

prototype

Producedynamic design

prototype

Evaluate designwith end-users

Implementfinal userinterface

Evaluate designwith end-users

Analyse andunderstand

user activities


Types of User Interface

There are different types of User Interface

1) Graphical User Interface (GUI)2) Menu User Interface3) Form based User Interface4) Command Line User Interface5) Natural Language Processing UI


Graphical user interfaces

This User Interface mainly relies on the use of window, icon, menus and pointer (WIMP). The use is able to select his/her options by use of menus of choices and by using small pictures (icons) which represent the different options available. These choices are basically selected by the user by using the pointer device such as mouse.


GUI characteristics

Characteristic DescriptionWindows Multiple windows allow different information to be

displayed simultaneously on the user’s screen.Icons Icons different types of information. On some systems,

icons represent files; on others, icons representprocesses.

Menus Commands are selected from a menu rather than typedin a command language.

Pointing A pointing device such as a mouse is used for selectingchoices from a menu or indicating items of interest in awindow.

Graphics Graphical elements can be mixed with text on the samedisplay.


They are easy to learn and use.

Users without experience can learn to use the system quickly.

The user may switch quickly from one task to another and can interact with several different applications.

Information remains visible in its own window when attention is switched.

Fast, full-screen interaction is possible with immediate access to anywhere on the screen



Menu systems

Users make a selection from a list of possibilities presented to them by the system

The selection may be made by pointing and clicking with a mouse, using cursor keys or by typing the name of the selection

May make use of simple-to-use terminals such as touchscreens


Example for Menu based interface


Advantages of menu systems

Users need not remember command names as they are always presented with a list of valid commands

Typing effort is minimal User errors are trapped by the interface Context-dependent help can be provided.

The user’s context is indicated by the current menu selection


Problems with menu systems

Actions which involve logical conjunction (and) or disjunction (or) are awkward to represent

Menu systems are best suited to presenting a small number of choices. If there are many choices, some menu structuring facility must be used

Experienced users find menus slower than command language


Form-based interface This type of user interface is where an operator is

inputting information while asking a customer questions over the telephone.

Prompts the operator to ask all the questions. Makes the user input the information in the

correct order and in correct format. It is user-friendly as the user is able type in the

specified areas in the form as the cursor moves to the next box once the current box is filled with correct data.


Example for Form-based interface

Title

Author

Publisher

Edition

Classification

Date ofpurchase

ISBN

Price

Publicationdate

Number ofcopies

Loanstatus

Orderstatus

NEW BOOK


Command interfaces Command line interfaces are one where the user

types series of commands at the keyboard which tell the computer what their intentions are.

The user should know previously all the commands which are available.

This user interface restrict the options that the user has available to them as it is mainly mean t for computer literate people.


Problems faced in Command line interfaces

Users have to learn and remember a command language. Command interfaces are therefore

unsuitable for occasional users Users make errors in command. An error

detection and recovery system is required System interaction is through a keyboard so

typing ability is required


Command languages

Often preferred by experienced users because they allow for faster interaction with the system

Not suitable for casual or inexperienced users

May be provided as an alternative to menu commands (keyboard shortcuts). In some cases, a command laCnguage interface and a menu-based interface are supported at the same time


Example for Command line user interface

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Natural language interfaces

The user types a command in a natural language. Generally, the vocabulary is limited and these systems are confined to specific application domains (e.g. timetable enquiries)

NL processing technology is now good enough to make these interfaces effective for casual users but experienced users find that they require too much typing

©ravichandranuser interface slide 1 user interface design

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