Data flow & information requirements

 Establishing IPSO  Recording information about the existing system  Identifying the problems with the system  Identifying User & Information requirements of the new system  Identifying HW & SW for a new system.

 Our analyst has collected information about the current system using questionnaires, observation, interviews and examining documents.  What happens next?

 Need to identify all the inputs, processing & outputs in the existing system.  How?

This allows the analyst to establish which documents relate to information coming IN to the system, and which relate to information going OUT.

 The analyst uses this knowledge to produce his own documentation of the system which helps him understand the system properly.

 ….needs to be examined to see the specific inputs, processes & outputs.  What would be the inputs of a payroll system?  The processes?  The outputs?

 All results of fact-finding must be recorded  Accurate records are vital – why?  Because the system will evolve  Other analysts & programmers will need to develop the system even further at some point in the future.

 Data flow diagrams  These are a graphical method of recording the inputs, processing & outputs that have been identified.

 Flow charts show the control flow of the program  DFDs show how the data flows around the entire system

 Data flow diagrams illustrate how data is processed by a system in terms of inputs and outputs.  Have four components:  Terminators  Processes  Flow arrows  Stores

Process order Customers Orders Rejected Orders Orders Invoices Invoice data Order Information

Customers A Terminator - someone or something outside the system (eg a customer or a supplier) Invoices Data stores – where stored on paper or on a computer Data flow. It is important that the direction of the flow is accurately recorded. Process order

 Level 0  Very generalised  Shows terminators linked to current system eg 0 Customers Order Processing system Customers

 Level 1:  Many more processes  More detail  Process boxes for both receiving orders and for producing invoices 1

 Level 2:  These show all aprts of the level 1 diagram in much more detail 2

 Represent the way that data flows around the existing (old) system

 May be used, but generally are found in the design stage.  Represent the new system – the one that is going to be designed & implemented.

 DFDs help the analyst to identify problems or weaknesses within the current system:  Eg data duplication  Job duplication  Unnecessary steps  Why is it necessary to identify these problems?

 DFDs help the analyst decide on:  Appropriate methods of input  Approximate processor speed & memory  Size & number of storage devices  Quantity & format of output

 The new system MUST meet the needs of the people who will use it  So – the analyst needs to know exactly what job each person does and what their requirements are.  He can the produce a Requirements Specification – a list of features of the system that are required.

 Step 1 : collecting information on how the current system works  Step 2 : Establishing inputs, processes & outputs  Step 3 : recording information  Step 4 : Identifying problems  Step 5 : Identifying suitable hardware & software  Step 6 : Identifying user & information requirements