Design f. describe a design specification including input design, diagrammatic depiction of the overall system, processing, data structure design and output design;

Top down design Top down design involves breaking down a large task into smaller (easier to solve pieces) Mobile Phone Voice Calls Receiving Voice Sending Voice Text messages Phone book

Modular program design Most of the programs you write will be fairly small but in industry programs can be tens of thousands of lines of code long. Windows Vista contains around 50 million lines of code Programming can be made easier by splitting the program into smaller modules. This is sometimes called the Divide and Conquer method.

Advantages of modular design 1.Some modules can be used many times in different programs. 2.It is easier to debug and understand a small module of code. 3.Maintenance is easier because it is easy to identify problem modules. 4.In a large project several programmers will work on the same program. Using the modular approach each programmer can be given a specific set of modules to work on.

Designing solutions The design will usually involve 3 stages: 1.Designing the user interface 2.Designing the data that is used in the program. 3.Designing the processing that needs to be done on the data.

A good user interface A good user interface meets three criteria: It is ……… Effective – Allows the user to input and output all the data correctly. This should reduce errors made by a user. Efficient – Makes the best use of the resources available to the program. Processor time etc This increases user productivity and prevents the user becoming frustrated. Satisfying – One that the end user enjoys using and is easy to learn. The user can focus on completing the task not on learning the new software.

Types of user interface 1.Command line interface 2.Graphical User interface (GUI) - Windows Icons Menus Pointers (WIMP) 3. Speech Recognition

Command line Example: DOS or the Linux Terminal Advantages: Very fast to use, require very little power to run. Disadvantages: Tricky to learn all the syntax, not very friendly for new users

Graphical User Interface Example: Windows, JellyBean Advantages: Much easier to learn to use, more intuitive Disadvantages: Slower than experienced Command Line users require much, more power to support and run.

Speech recognition Example: Siri Advantages: Good for short phrases like “CALL MUM” Disadvantages: difficult to carry out more complex operations.

Data requirements of a program When designing a system you need to specify what data the program will need and how it will be stored. This is usually done in a Data Dictionary. IdentifierData TypeSizeValidation PasswordString32 BitMust be more then 6 characters UsernameString32 BitMust be unique in the system

Flowcharts Start or Stop Process Decision

Pseudo Code Pseudo Code is just simplified code. It allows the author to focus on the logic behind the problem instead of the syntax of a particular language. BEGIN INPUT Password IF Password = StoredPassword Then AccessSystem() ELSE Message(Password incorrect) END IF END

Real code Notice that the basic logic is the same as the Pseudo code but the syntax is correct for Visual Basic. Public Sub PasswordCheck(Password as String, StoredPassword as String) If Password = StoredPassword Then AccessSystem() Else Msgbox(“Password Incorrect”) End If End Sub

Jackson diagrams Jackson Structure Diagrams are used to represent the structure of a program. Step 1: Break the Program down into its component modules. AcountzPro Edit Record Calculate Output Result Delete Record YesNo

Step 2: Show any Selective statements (IF, Case etc) Delete Record YesNo

Step 3: Show any Iterative statements (Loops) Calculate* Result Output Result While X > 3