Data Flow Diagrams DFD Data Flow Diagrams DFD
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Data Flow Diagrams (DFD)
Data Flow Diagrams (DFD) 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. Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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 Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) Symbols A DFD will include all of the following symbols: ‘Data Stores’ ‘External Entity’ ‘Data Flows’ ‘Process’ Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) External Entities are used to represent people, organisations or other systems. ‘External Entity’ If an external entity is used twice, then a line is drawn through it These external entities play a part in the system, although are not a part of it. They either ‘input’ or ‘receive’ data. Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) Processes 3 A process represents an activity that takes place within and is linked to the system. Order Process All activities within a system have a process attached to them (eg its like a doing symbol). ‘Process’ Note: can have any number of inputs and outputs linked to it. A process models what happens to the data Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) Data Stores A data store shows where data is stored. D 1 ‘Data Stores’ D 1 If a data store is used more than once, then an additional vertical line is added above 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. Note: a ‘D’ represents a computerised data store and an ‘M’ represents a manual data store (eg filing cabinet) Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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 Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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 Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) Rules that you need to follow below: Data Flow Links Data Store External Entity Process Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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 Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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) Steps 1 2 3 4 5 Processes (eg Data Activities) External Entity Applicant (Completes application form Credit Check Agency Applicant (Letter sent to applicant confirming account details Data Stores Application form Inspected Input Applicant information Create applicant account Perform security checks (eg outside credit check) Applicants Accounts Generate letter to be sent to applicant with new account details on Applicant Accounts Data Flow Table Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) Example: bank account Completed Forms 1 Inspect Forms Applicant Forms filled in wrong Validated Forms 2 Input Applicant Informat. Applicants Applicant information entered 3 Accounts Applicant Letter sent to applicant 5 Generate letter to be sent to applicant with account details on Applicants Accounts Credit check confirmed 4 Create Applicant Account Applicant account created Data Flow Diagrams (DFD ) Perform security Checks (eg credit check Credit Check Agency A Level ICT
Data Flow Diagrams (DFD) Exercise 1: DFD Exercise See if you can correct and create some small DFD diagrams Data Flow Diagrams (DFD ) A Level ICT
Data Flow Diagrams (DFD) 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) Data Flow Diagrams (DFD ) A Level ICT
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