DATA FLOW DIAGRAM

DATA FLOW DIAGRAM

A  DFD , also known as a  “bubble chart “ serves the purpose of clarifying system requirements and identifying major transformation that become program in system design . A DFD consists of a series of bubbles joined by lines . the bubbles represent data transformation and lines represent data flows in system . the DFD is a representation of various processes and the input and output in each process . Graphical description of a system’s data and how the process transform the data is known as Data Flow Diagram (DFD).

  

Data Flow Diagramming is a means of representing a system at any level of detail with a graphic network of symbols showing data flows, data stores, data processes, and data sources/destination.

The data flow diagram is analogous to a road map. It is a network model of all possibilities with different detail shown on different hierarchical levels. This processes of representing different details level is called “leveling” or “partitioning” by some data flow diagram advocates. Like a road map, there is no starting point or stop point, no time or timing, or steps to get somewhere. We just know that the data path must exist because at some point it will be needed. A road map shows all existing or planned roads because the road is needed.

 Details that is not shown on the different levels of the data flow diagram such as volumes, timing, frequency, etc. is shown on supplementary diagrams or in the data dictionary. For example, data store contents may be shown in the data dictionary.

  

 Terms used in DFD

 

Process  : A process transforms data values  The lowest level      processes are pure  functions without side effects  An entire data flow   graphics  high level  process.

Data flows : A data flow connects the output of an object or process to input of another object or process. It represents the intermediate data value within a computation. It is represented by an arrow and labeled with a description of data, usually its name or type.

Data store  :  A data store is a passive object with in a data flow diagram that   .

stores data for later access

External Entity   A rectangle  represents an external entity such as a librarian                       

a library member

Symbols Used in DFD 

Square                                                    

A square defines a source (originator) or destination of system data.

Arrow                        

An arrow identifies data flow-data in motion. It is a pipeline through which information flows

Circle

                    

A circle or a bubble represents is a process that transforms incoming data flow into outgoing data flow. Circle basically represents a process.

Open Rectangle

 An open Rectangle is data store-data at rest, or temporary repository of data. Open rectangle basically denotes data storage.

 

Naming  Conventions in DFD

The name of data stores and destination are written in capital latters . process and data flow name have the first letter of each work capitalize

                              CONTEXT LEVEL  OR  0 LEVEL DFD