Data Flow 2

Identifying Data Flows During the analysis stage of a project it is important to find out how data flows through a system: Where does the data originate What processing is performed on it and by whom Who uses the data What data is stored and where What output is produced and who receives it

DATA FLOW DIAGRAMS [DFD’S] A diagram to show how data is captured, processed , stored and distributed within a system. This is generally represented during the analysis stage of a project, but can be further refined during the design stage to show more detail of how the system functions.

E.g. Result of a query to a database, contents of a printed report : data that moves together to common destinations Actions performed on data so that they are transformed, stored or distributed. This can be a computerised or manual transformation SYMBOLS USED IN A DFD PROCESS DATA FLOW

A physical location to hold data e.g. a file folder or notebook etc. Origin and/or destination of the data. Often referred to as external entities as they are outside the system. We are only interested in how data flows in to or from the system to them. SYMBOLS USED IN A DFD DATA STORE SOURCE/SINK

It is often impossible to represent a complete business on one diagram. For this reason it is quite common to use more than one level of Data Flow Diagram with each level showing more detailed information about part of the previous diagram. It is important that the diagram should be made as clear as possible and for this reason it is not uncommon to draw the same source or sink [external entity] more than once to help achieve this. How Much Detail ?

Main steps when constructing a Level 0 Diagram : Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled Context or Level 0 Diagram The highest level view of a system. This only has one process which represents the overall function of the system and has no data stores as all the data is stored within the process.

Constructing a Level 1 diagram Identify and draw the processes that make up the Level 0 process Allocate descriptions to these Lay out the sources/sinks and data flows from the Level 0 diagram Draw in any data stores used in the process Link the new processes and data stores with named data links

IF it is necessary to produce a level 2 or level 3 diagram, the same steps would be followed as used when constructing the Level 1 diagram Constructing a Level 2/3 diagram

Here is an example of how Data flow diagrams would be used to model the logic of data flows in a fast food burger bar. Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled . Context or Level 0 Diagram

Level 0 Context diagram CUSTOMER

Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out in a diagram using the correct symbols Link them with data flows that are labelled

CUSTOMER Level 0 Context diagram KITCHEN RESTAURANT MANAGER

CUSTOMER KITCHEN RESTAURANT MANAGER Level 0 Context diagram Food ordering system 0

Identify where data is captured from Identify where data is distributed to Describe the overall process Map these out using the correct symbols Link them with data flows that are labelled

Food ordering system 0 CUSTOMER KITCHEN RESTAURANT MANAGER Level 0 Context diagram Food Order Management Reports Customer Order Receipt

Food ordering system 0 CUSTOMER KITCHEN RESTAURANT MANAGER Food Order Management Reports Customer Order Receipt Level 0 Context diagram Does this show enough detail?

These new processes may show a process which corresponds to actions such as : Capturing data from different sources Maintaining data stores Producing and distributing data to different sinks Level 1 diagram

1.0 Receive and transform Customer Food Order

These may show a process which corresponds to actions such as : Capturing data from different sources Maintaining data stores Producing and distributing data to different sinks Level 1 diagram

1.0 Receive and transform Customer Food Order 2.0 Update Inventory file 3.0 Update Goods Sold file

1.0 Receive and transform Customer Food Order 2.0 Update Inventory file 3.0 Update Goods Sold file 4.0 Produce Management Reports

1.0 Receive and transform Customer Food Order 2.0 Update Inventory file 3.0 Update Goods Sold file 4.0 Produce Management Reports KITCHEN Food Order CUSTOMER Customer Order Receipt RESTAURANT MANAGER Management Reports

RESTAURANT MANAGER Food Order Customer Order Receipt Management Reports 1.0 Receive and transform Customer Food Order 2.0 Update Inventory file 3.0 Update Goods Sold file 4.0 Produce Management Reports CUSTOMER KITCHEN Goods Sold File D1 D2 Inventory File

RESTAURANT MANAGER Food Order Customer Order Receipt Management Reports 1.0 Receive and transform Customer Food Order 2.0 Update Inventory file 3.0 Update Goods Sold file 4.0 Produce Management Reports CUSTOMER KITCHEN Goods Sold File D1 D2 Inventory File Goods Sold Inventory Data Goods Sold Data Inventory Data Daily Goods Sold Amount Daily Inventory Depletion Amounts

In this example, having constructed our Level 1 diagram it is decided there is no need to further breakdown the data flow processes within this organisation. Our data flow diagram is therefore complete.

Do’s and Don’ts when constructing a Data Flow Diagram  

Data Flow 2

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Data Flow 2