A data flow diagram (DFD) maps how data moves through a system. It shows how data entering the system (input) is transformed (process) and changed into something new (output) The DFD shows how data is stored in a system, using data stores.

A data flow diagram (DFD) will also show what and who a system interacts with in the form of external entities. These external entities could be: People Other Systems

‘Data Stores’ ‘Data Flows’ ‘Process’ ‘External Entity’ Symbols A DFD will include all of the following symbols:

‘External Entity’ External Entities External Entities are used to represent people, organisations or other systems. These external entities play a part in the system, although are not a part of it. They either ‘input’ or ‘receive’ data. If an external entity is used twice, then a line is drawn through it

‘Process’ Processes A process represents an activity that takes place within and is linked to the system. All activities within a system have a process attached to them (eg its like a doing symbol). A process models what happens to the data Order Process 3 Note: can have any number of inputs and outputs linked to it.

‘Data Stores’ Data Stores A data store shows where data is stored. Examples of data stores include a database file, a filing cabinet and a lever arch folder. A database store should be given a meaningful descriptive name. D1 If a data store is used more than once, then an additional vertical line is added above Note: a ‘D’ represents a computerised data store and an ‘M’ represents a manual data store (eg filing cabinet)

Data Flows A series of data flows indicate the direction of data as it moves around the system. The data flows provide meaningful links between DFD symbols. They too should be given meaningful names ‘Data Flows’

Data Flows A series of data flows indicate the direction of data as it moves around the system. The data flows provide meaningful links between DFD symbols. They too should be given meaningful names ‘Data Flows’

Rules that you need to follow below: Data Flow LinksData StoreExternal EntityProcess Data Store External Entity Process

How to create a DFD? You can use the following sequence: 1.Investigate and analyse the current system 2.Create a data flow table from the above research 3.Convert the table into DFD symbols 4.Join the symbols together with data flows

This is a data flow table to organise the order of outside activity (eg external entity), data activities (eg processes) and storage activity (eg data stores) StepsExternal Entity Processes (eg Data Activities) Data Stores 1  Applicant (Completes application form  Application form Inspected 2  Input Applicant information  Applicants 3  Create applicant account  Accounts 4  Credit Check Agency  Perform security checks (eg outside credit check) 5  Applicant (Letter sent to applicant confirming account details  Generate letter to be sent to applicant with new account details on  Applicant  Accounts Data Flow Table

Applicant Inspect Forms 1 Input Applicant Informat. 2 Create Applicant Account 3 Perform security Checks (eg credit check 4 Applicants Completed Forms Forms filled in wrong Validated Forms Accounts Applicant information entered Applicant account created Credit Check Agency Credit check confirmed Generate letter to be sent to applicant with account details on 5 Applicant Applicants Accounts Example: bank account Letter sent to applicant

Exercise 1: DFD Exercise See if you can correct and create some small DFD diagrams

Exercise 2: Signing up to a sports club See if you can create a DFD to sign up to a sports club. (There is not necessarily a right or a wrong answer, but in this case use the symbols provided)