DATA FLOW DIAGRAM

Posted by dhee Saturday, April 4, 2009 comments (0)

The idea of a chart to represent data in a system that is not new. In the year 1967, Martin and Estrin introduce an algorithm program by using the circle and arrow symbols to represent data flow. E. Yourdan and L.L. Constantine also use this notation symbols to describe the flow of data in the design program. GE Whitehouse 1973 also use the notation to make this kind of model system
mathematics. The use of notation in the data flow diagram is very helpful to understand at all levels complexity such as that expressed by Chris Gane and Trish Sarson. The data flow diagram describing the system modules in a smaller part. Easily the less understood areas of the computer to understand the system that will be done.


Context Diagram
Context diagram consists of a process and describe the scope of a system and it is the highest level of the DFD that describes the input to and output from the entire system. The system is limited by boundary (depicted by broken lines) and there is no storage (storage).


Zero Diagram
Zero diagram describes the process of the DFD. It's provides a view of the overall system, showing the main function or process that is, and the showing the flow of data and external entity. At this level, the data storage is possible. The process is no longer detailed on the next level then added the symbol '*' or 'P' at the end of the process. The input and output balance between zero diagram and context diagram should be maintained.


Detailed Diagram
Detailed diagram is a diagram which explain the process in the zero diagram or above. Numbering level in the DFD is as follows:






Symbols That Used to DFD
Some of the symbols used in the DFD are as follows:
1. external entity or boundary
2. data flow
3. process
4. data store


1. External Entity
Each system has certain boundaries that separate a system with the environment outside the system. The system will receive input and produce output to the outside environment. External entity is an entity in environment outside the system that can be a human being, organization, or the other system. Most external entity is one of the following:

  1. An office, department or division in the company but outside the system that is being developed.
  2. Person or a group of people in the organization but outside of that system is being developed.
  3. An organization or a person outside the organization such as customer and supplier.
  4. Other information systems outside the system that is being developed.
  5. Original source of a transaction.
  6. Recipient of a final report produced by the system.

External entity can symbolized with a notation box.





2. Data Flow
Data flow is a place of information flow. Data flow depicted with a straight line connecting the components of the system. Data flow is shown with the direction arrows and the name on the flow of data that flows. The data flow is pour between processes, storage data, and its indicates that the form of data input for the system.
Here are some examples of data flow:
a. Forms or documents used in the company.
b. Printed reports generated by the system.
c. Display or output on a computer screen generated by the system.
d. Input to the computer.
e. Speech communication.
f. Letter or memo.
g. Data is read or recorded to a file.
h. A field note book on the agenda.
i. Transmitting data from one computer to another.
Flow data should be given the name and have a clear meaning. The name of the data flow in addition to the written its arrow. Following example:



Guidelines for naming:
1. The flow of data flow consists of several words associated with the line speed
2. No data flow of the same name and should reflect the contents
3. Flow of data that consists of several elements can be expressed with the group element
4. Avoid using the word 'data' and 'information' to give a name to the flow of data
5. Wherever possible the complete flow of data is written



3. Process
A process is an activity or work done by the person, machine or a computer from the result of data flow into the process for generated data that will flow out of the process. The process is what is done by the system and then can process data flows or data entry into the flow of data out. The transform function of one or more of data input into one or more of the output data in accordance with the desired specifications so each process has one or more inputs and produce one or more output. The process is also called bubble.
A process can be indicated with a circle symbol or rectangle with straight corners blunt.


Each process must be given a full explanation include the following.
  1. Identification process. This included the identification of a number that indicates the number of reference and the process is written at the top of the symbol in the process.
  2. Name of the process. The name indicates that the process is done by the process. Name of the process must be clear and complete.
  3. Processor. The processor may not be listed.

Guidelines naming of the process:
  1. The process consists of a verb and noun, which reflects the function of the process.
  2. Do not use the process as part of the name of a bubble.
  3. There may be some process that has the same name.
  4. The process must be given a number. Order number wherever possible to follow the flow of the process or sequence, but the sequence number does not mean that the absolute is a process in chronological order.



4. Data Store
Data storage is a storage place for data that exists in the system.
Symbolized with a pair of parallel lines or two lines with one side open side. The process can retrieve data from or provide data to the database.
Guidelines for naming:
1. The name should reflect the data storage.
2. When its name more than one word must be marked with the number.

Data store can be as follows:
a. A file or database in the computer system.
b. An archive or records manual.
c. A box of data.
d. A table reference manual.
e. Agenda or a book.



DFD SYMBOL






Type of Data Flow Diagram
There are 2 forms of DFD, the physical data flow diagram and logical data flow diagram. Physical data flow diagram more emphasis on how the process of the system is applied while
logical data flow diagram is to emphasize the process of what is found in the system.
  1. Physical Data Flow Diagram, more appropriately used to describe the existing system. The emphasis on this diagram is how the processes of the system is applied. PDFP must include the following:
    1. Manual processes are also described.
    2. Name of the flow data must indicate the number of such application form and the medium.
    3. Savings data can show savings of non-computer.
    4. The name of saving the data type of application must show, whether manual or computerized.
    5. The process must show the name of the processor, the man, ministry, computer system or computer program to access the process.
  2. Logical Data Flow Diagram, more appropriately used to describe the system that will be proposed. LDFD does not emphasize on how the system implemented, but the emphasis only on the logic of the needs of the system.
For computerized systems, drawing LDFD that shows only the needs of the proposed logic of system, usually the processes described is only the computer proces only.



Data Dictionary

Data dictionary is to help the system to interpret the application in detail and organize all elements of the data used in the system precisely so that the system analyst have a basic understanding of the same input, output, storage and process.
At analysis step, the data dictionary is used as a means of communication between the systems analyst with the user, and at the design stage of the system, the data dictionary is used to design input, reports and databases. Load the data dictionary as follows:
  1. The flow of data: should be noted that readers who need further explanation about a flow of data can find it easily.
  2. Alias: alias or other name of the data can be written when it is existence.
  3. The form of data: used to segment the data dictionary to use when designing the system.
  4. Data flow: indicates from which data flows and where the data goes.
  5. Description: provides an explanation about the meaning of the data flow.



Balancing in DFD

Balancing in DFD means flow of data into and out of a process must be the same as the flow of data into and out of the details of the process on the level/levels below. Besides then the flow of data into and out of the process must match the name of the flow of data into and out of the details of the process. The number and name of an entity outside the process must be equal to the number of names and entities outside of the details of the process.
There are some issues that must be considered in the DFD which have more than one level:
  1. Must be balance between input and output of one level and next level.
  2. Balance between level 0 and level 1 at the input / output of stream data to or from the terminal on level 0, while the balance between level 1 and level 2 is seen on the input / output of stream data to / from the process concerned.
  3. The flow of data, the data storage and the terminals at each level must be the same if its the same object.


Prohibition in DFD
  1. Flow data may not be from outside the entity directly to other outside entities without going through a process.
  2. Flow data may not be from the savings directly to the data to outside entities without going through a process.
  3. Flow data may not be saving the data directly from the other savings data without going through a process.
  4. Flow of data from one process directly to the other without going through the process of saving data should or be avoided as much as possible.