DATA FLOW DIAGRAMS
Data flows are data structures in motion, while data stores are data structures. Data flows are paths or ‘pipe lines’, along which data structures travel, where as the data stores are place where data structures are kept until needed.
Data flows are data structures in motion, while data stores are data structures at rest. Hence it is possible that the data flow and the data store would be made up of the same data structure.
Data flow diagrams is a very handy tool for the system analyst because it gives the analyst the overall picture of the system, it is a diagrammatic approach.
A DFD is a pictorial representation of the path which data takes From its initial interaction with the existing system until it completes any interaction. The diagram will describe the logical data flows dealing the movements of any physical items. The DFD also gives the insight into the data that is used in the system i.e., who actually uses it is temporarily stored.
A DFD does not show a sequence of steps. A DFD only shows what the different process in a system is and what data flows between them.
The following are some DFD symbols used in the project
Process: A transaction of information that
resides within the bounds of the system
to be module.
DATASTORE: A repository of data that is to be stored for use by one or more processes, may be as simple as buffer of queue or as a relational database.
RULES FOR DFD:
· Fix the scope of the system by means of context diagrams.
· Organize the DFD so that the main sequence of the actions reads left to right and top to bottom.
· Identify all inputs and outputs.
· Identify and label each process internal to the system with rounded circles.
· A process is required for all the data transformation and transfers. Therefore, never connect a data store to a data source or the destinations or another data store with just a data flow arrow.
· Do not indicate hardware and ignore control information.
· Make sure the names of the processes accurately convey everything the process is done.
· There must not be unnamed process.
· Indicate external sources and destinations of the data, with squares.
· Number each occurrence of repeated external entities.
· Identify all data flows for each process step, except simple Record retrievals.
· Label data flow on each arrow.
· Use details flow on each arrow.
· Use the details flow arrow to indicate data movements.
· There can’t be unnamed data flow.
· A data flow can’t connect two external entity.
LEVELS OF DFD:
The complexity of the business system means that it is a responsible to represent the operations of any system of single data flow diagram. At the top level, an Overview of the different systems in an organization is shown by the way of context analysis diagram. When exploded into DFD
They are represented by:
· LEVEL-0 : SYSTEM INPUT/OUTPUT
· LEVEL-1 : SUBSYSTEM LEVEL DATAFLOW FUNCTIONAL
· LEVEL-2 : FILE LEVEL DETAIL DATA FLOW.
The input and output data shown should be consistent from one level to the next.
LEVEL-0: SYSTEM INPUT/OUTPUT LEVEL
A level-0 DFD describes the system-wide boundaries, dealing inputs to and outputs from the system and major processes. This diagram is similar to the combined user-level context diagram.
LEVEL-1: SUBSYSTEM LEVEL DATA FLOW
A level-1 DFD describes the next level of details within the system, detailing the data flows between subsystems, which makeup the whole.
LEVEL-2: FILE LEVEL DETAIL DATA FLOW
All the projects are feasible given unlimited resources and infinite time. It is both necessary and prudent to evaluate the feasibility of the project at the earliest possible time. Feasibility and the risk analysis are pertained in many ways. If project risk is great.