SE Process Q & A #4


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Question:Explain concept of data flow diagram.

Answer:

Data flow diagram

Data flow diagram has two points.

  1. Depict the data flow through the system.

  2. It shows the needs of the system in a graphical form.

Here a system may be defined as a company, organization, process, a hardware and software system of computers etc.

Objectives of DFD

  • It gives the detail of data flow.

  • It gives the information about hierarchical breakdown of the system.

  • DFD gives the detail of used file and result flow.

  • Flow of document information in system.

For understanding a system, DFD is very helpful during the analysis process. The DFD has an advantage of simplicity and is easy to use. With the help of graph a good communication is built between user and analyst. There are some considerations which are helpful in developing a DFD.

Symbols used in making DFD

A limited number of symbols are used in a DFD to represent those functions which is done by a system and flow of data between these functions. Details of symbols are given below:

  • External entity symbol - The external entity symbol represents sources of data to the system. A rectangle represents an external entity. An external entity have no responsibility for any action done by the system.

  • Data flow system - For the presentation of data flow, arrow symbol is used. It shows the complete detail of data which data is used in processing. The flow of data can be use in two processes. Data flow system show the name and direction. Several types of element find in a data flow. For Example: - A data flow name is bank account it may consist of elements just like customer name, date of birth, nominee name, amount etc.

  • Functional system - The circular shape is used to represent a function graphically represent. Some experts use oval or rectangle for the representation of functional symbol. The second name of the function is bubble or transformation to perform some task with the data it convert or transferred data from one computer to other. A name is very necessary for this which can define what function does? Every process has a specific number which start from up to down and left to right.

  • Data store symbol - A data store may be defined as an open rectangle. A data store is stored permanently data for performing transactions. Every data store connected with process. A data store may take place on a disk with a logical file or physical file to report it.

DFD Symbols

Guideline for the DFD

A DFD have no any standard method for developing it for the problem given. Some of the steps are given below for making a DFD.

  • A data diagram is made.

  • Divide the data in 2 or 3 data levels.

  • Divided the second level data in elementary level data which have all the information of actual process.

Context diagram

A diagram has only one process which represents the whole system, which is called context diagram. This type of DFD is used on high level.

Detailed level DFD

Where the text is divided on elementary level by DFD symbols then it is called detailed level DFD.

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