Software Development

Chapter 2

Interface Design

Need For User Interface

Various people from different backgrounds now use computers in everyday life

The need for a user friendly interface which the average person can productively interact with is important

This need led to the development of various types of user interfaces, categories for different types of users

The vast majority of programs are now interactive and user interfaces are often graphical

Types Of User Interfaces There are many different types of user interfaces currently in use

Each type of interface can be characterised by the style of interaction it supports

The most common styles include: Command Driven Menu Drive Graphical User Interface (GUI) Special Purpose

Styles are chosen by designers to support the particular tasks

Many systems have a mixture of styles to support different tasks

Command Driven-

The command line interface was the first interactive user interface

They do not require much effort in screen design or management as a basic black or white background with contrasting text is normally used

Commands are entered at a prompt and validated by the command language interpreter before being carried out

Commands are words or mnemonics as the amount of typing should be minimal

Command Line Interpreter (CLI)

CLI Advantages

They may be implemented using cheap alphanumeric displays

More experienced users have direct control over the operations

Commands of almost arbitrary complexity can be created by combining individual commands

It is faster to issue a command sequence directly rather than searching through a menu

It allows complicated and sophisticated operations to be performed and combined with scripts

CLI Disadvantages

Users have to learn a command language that can be complex

The learning time for a CLI is greater

Users always make mistakes in typing, this requires error handling and message generation facilities

System interaction is through a keyboard

It can be difficult to get the simplest operations performed

Commands across different operating systems are different

Menu Driven

Menu driven interfaces present the user with a list of options

The user can make their selection from a keyboard or pointing device

Selecting an option may initiate a command or present the user with a sub-menu Sub menus are said to be nested inside the menu

There are three major categories menus can be divided into: Full Screen Menus Bar and Pull-Down Menus Pop-Up Menus

Full Screen Menus

These menus present the options to the user as a sequential list

It is followed by a message prompting the user to select one

Options may be numbered or a letter used to uniquely identify each option and to facilitate quick selection

Bar and Pull-Down Menus The main options available to the user are presented as pads on a horizontal bar

across the screen

When the user selects a pad the second-level options are displayed in a pull-down menu

This type of men system is used in with a pointing device

Options may also be selected using shortcut or arrow keys

Pop-Up Menus

These menus appear as a box with one of the options already selected

When the user points to the box the other options are displayed in a list and the user can select one with the pointing device

Menu options only remain visible when the pointing button is depressed

Menu Driven Advantages

The user is presented with a choice so does not need to remember commands

The interface is suitable for beginners

The opportunities for making serious errors are reduced

Menus can utilise special pointing devices keeping typing to a minimal

Menu Driven Disadvantages

They are not as concise as command driven interfaces

Accomplishing a task in a menu driven interface involves more steps than a command driven interface

If there is a large number of options available it is difficult to structure the menu system

Tasks which involve logical operators are awkward to express

Graphical User Interface

The main elements of a GUI are: Windows Icons Menus Pointers Alerts and Warnings Dialogue Boxes

WIMP

The first four elements of a GUI were responsible for the term WIMP being applied to these type of interfaces

Using a WIMP environment allows the user to directly manipulate objects and perform operations

Windows

A window is an interface component through which objects and actions are presented

It is an area of the screen dedicated to a specific purpose

Windows may be tiled or overlapping

They can be moved around and resized

Windows may also be scrolling

Icons

An icon is a pictorial representation of an object or action

A unique icon represents an application when it is minimised

Icons must be understandable by users and its purpose must be clear to users

Menus

The graphical user interface can support all types of menus

Common types are: Pull-Down Menus Menu Bars Scrolling Menus Pop-Up Menus

Pointers

A pointer is a symbol displayed on the screen that is controlled by a pointing device like a mouse

It is used to point at objects and action on screen that the user wants to select

The pointer is the tool used to drive the GUI

Alerts and Warnings

Alerts and warnings occur as pop-up menus

They notify the user of an event that requires a response

The user can choose between overriding the event or by performing the required action

Dialogue Boxes

A dialogue box is a movable window in which users provide information that is required by an application so it can perform the user request

Processing Capabilities of a GUI

The graphical nature of a GUI gives it the ability to perform a variety of different operations

This includes combining text and graphics

Graphical Operations

Some operations of a GUI are: What You See Is What You Get (WYSIWYG) editing

Refers to the representation of an image on screen being an exact image of the end result

Image scanning Processable graphics Animation and support for multimedia

The manipulation of graphics to produce moving images is called Animation Porting of documents or files across different applications

A GUI treats all files as objects, making it possible to embed one object within another. So you can use a file created in one application in another

Provisions for users with disabilities The WIMP environment is ideally suited for adjusting components for users

with visual, hearing or mobility difficulties

GUI Advantages

Users feel in control of the computer

User learning time is short

Immediate feedback on actions is given so mistakes can be detected and corrected quickly

Icons help users to recognise what objects are meant to represent

Users can transfer skills from one WIMP based operating system to another

GUI Disadvantages

Interfaces are processor intensive and memory demanding

Powerful and expensive processors are needed to support tasks

Sometimes a longer sequence of steps is necessary to perform certain operations in a GUI

Screens can become cluttered and difficult to navigate

Special Purpose Languages

With the ever increasing development of hardware and software many specialised user interfaces are now being created

Interface Areas of Use

Touch screens Museums Allows users to navigate menu system of art works, etc. by touching screen with finger.

Speech Visually and physically disabled users

Users can get audible sounds and words from the computer.

Natural language Speech input systems

The most natural interaction style. Speech recognition software is improving greatly but is still not perfect.

Pupils questions -

During the design phase careful consideration will be given to the design of theuser interface as well as producing a design of the detailed logic of the software.

(i) State three factors that will influence the project team when designing theuser interface for software accessed on the World Wide Web.

(ii) Pseudocode is used to represent the detailed logic of the proposed software.Describe three aspects of pseudocode that will assist the implementationof the system.

A company decides to offer DVD rental through the World Wide Web. Afterregistering, a customer will create a list of movies that he or she would like to watch. The highest positioned available movie from the list will be posted to the customer.When finished with the DVD, the customer will post it back. The management of the company decide to appoint a project team to oversee the implementation of a software solution.

Answer

(i) • Clients skill level.• Existing documentation indicating user current experience.• Existing software indicating staff’s current experience/skill.• Development environment.• Hardware and software (OS) that the software will run on.• Types of browser used to access as they have different capabilities eg layers, tables.• Minimum bandwidth since this will affect users’ ability to view graphics, video.• Any other acceptable answer. 1 mark for each of 3 factors

(ii) • English statements which have a one to one mapping with code (1).• Numbering reflects dependency (1).• Indentation to indicate control structures such as repetition and selection (1).• Data flow informs parameter passing (1).