Chapter3: System Design

Systems Design

Using the list of requirements, the systems analyst now has to design the new system.

The new system will be computer-based. The ease with which computers can communicate and process data means that are usually the best tool for the job.

Designing the System Inputs

To get data into a system is a two-part process:

Data must first be ‘captured’ (collected in a way that then makes it easy to input)
Data must be input into the computer

The systems analyst will select a data capture method and data input method that best suit the requirements of the new system.

Choosing the Best Data Capture and Data Input Methods for the System

Collecting data into a form that is ready for input to a computer system can be done in many ways

- Paper Forms

Form can be a simple ones with spaces for numbers and text to be written in. The data from this form would then be typed into the computer .Forms can also be machine-readable, such as OMR forms

- Barcode Reader

Barcode readers capture the numeric code that the barcode represents.

Typically used with POS systems and also stock-control systems.

- Card Reader

Many cards contain data stored on a magnetic strip or in a small bit of memory (smart cards) which can be captured with a card reader.Used in systems such as EFTPOS

Camera

Capture still or moving images which can then be input to a computer for processing.

In the payroll example, the hours worked by the employees could be captured using:-

A paper form (a timesheet) - simple and cheap, but the needs to be manually input (slow) and the form can be lost
Barcode reader - employees could have ID cards and swipe them at the start and end of work (can cheat easily)
Fingerprint reader - employees could put a finger on the reader at the start and end of work .

Designing On-Screen Forms for Data Input

Much of the data that enters computer systems needs to typed in. A well-designed on-screen form can make this task easier and quicker.

On-screen forms should...

Have all of the necessary fields
Have obvious places for user input (boxes, use of colour, etc.)
Use appropriate controls (see below) for each field
Have text box controls that are the right size for the data
Have easy-to-understand instructions (if needed)
Make good use of the screen area available

Form Controls

On-screen forms can have a variety of controls (the little buttons / boxes that you click or type in):

Textbox :Used for normal text input

Buttons :Used to perform an action

Option / Radio Buttons:Used to select an option (only one can be picked)

Tick / Check Boxes: Used to select options (more than one can be ticked)

Drop-Down Menus: Used to select options from a list

As data is entered into the form, it needs to be checked for accuracy. Two techniques help us do this: validation and verification.

Data Validation Techniques

When data is input to a computer, it is a good idea for the computer to check that the data is sensible (no dates of birth in the future, etc.)

Checks like this are called validation checks (is the data valid?)

Different validation checks can be used on different fields, depending on the type of data being entered.

Data Verification Techniques

Data validation only checks whether the data entered is sensible - it does not mean that the data is the right data. For example, if you are entering a date of birth and you mis-type it…

Correct date of birth: 12/11/1982
Date of birth entered: 12/11/1928

To check that data is the correct value, we use a system called data verification.

There are two methods of data verification:-

Designing the System Processes

Any system has to process the data it is given. The system designer has a number of things to consider...

Designing Data and File Structures

A data structure is an organised collection of data. Most commonly, this will be some sort of database in which data will be stored as it is being processed.

When designing a database, the system designer needs to consider:

The type of data being stored (numbers, text, dates, etc.)
The size of the data (how long is a typical name, etc.)
The field names to use
How many records will need to be stored

The designer also need to consider which backing storage device and media will be suitable to store the data:

How often will the data need to be accessed
How quickly the data needs to be accessed
How large will the data files be

So, for example, if there is a large amount of data that needs to be accessed quickly, and regularly, then a hard drive would be the best storage device to use.

Designing the How the Data Will be Processed

Of course, the system designer also needs to design the actual steps to be followed to processing the data Designing the How the Data Will be Processed.

Designing the System Outputs

There are usually two types of output from a system that need to be designed:

On-screen reports (information displayed on the monitor)
Printed reports (hard-copy to be mailed, filed, etc.)

Designing On-Screen Reports

Designing an on-screen report is similar to designing an on-screen form .There are a number of things that the designer should consider.

On-screen reports should...

Show all of the necessary fields
Have fields that are the right size for the data
Have easy-to-understand instructions (if needed)
Make good use of the screen area available
Make good use of colours and fonts to make the data clear

This is an example of a well-designed on-screen report used to show details of an employee…

Designing Printed Reports

Designing a printed report is just like designing an on-screen report ,except that the report needs to fit a piece of printer paper, rather than the screen. The report might also include page numbers, a header / footer.

This is an example of a well-designed printed report used to show details of an employee…