DATA FLOW DIAGRAM (DFD)
1. DFD usually use to figured a system division into smaller module and can make user to easy that insufficiently understand computer area for understands system who will be worked. A data-flow diagram can be used for the visualization of data processing (structured design).
DFD'S makings steps :
- Identification all outer unity that involved with system.
- Input identification and output what do be engaged extern unity.
- Make picture of diagram context.
Context diagram is upstairs diagram, constituting diagram of one system which figure data flows in going and sticking out of system and ingoing and sticking out from entities extern. Thing Who shall be noticed:
- Consist of a process and drawing a scope of a system.
- That is highest level of DFD, which it is drawing all of input to system and output of system.
- System limited by boundary (is depicted by dash line).
- No storage.
3. Zero Diagram is a diagram to describe process of data flow diagram. Zero Diagram is Providing views on the overall system in which, showing the main function or process that is, the flow of data and external entity.in this level may be existence storage data. For process which not detailed again in next level added by symbol ‘*’ or ‘ P’ in the end process number. Input balance and output (balancing) between diagram 0 with context diagram have to be maintain.
- Describe the process from DFD.
- Perhaps in this level can be storage data.
- For a process, which not dividing again in next level, so we can add symbols '*' or 'P' in the last process numbers.
- Balancing of input and output between zero diagram and context diagram have to be looked after.
- That is a diagram, that loosen all process in zero diagram or level before.
- Numbering level in the system.
- In a level, should nothing more than 7 process and maximal 9, if more that it, so we must decomposising.
Specification of Process
- Every process in DFD must have process specification.
- In top level method that used for describing process with descriptive sentence.
- In detail level that is in bottom process (functional primitive) requiring specification more structured.
- Process specification can be guide for programmer in coding.
- Method that used in process specification: explain process in narrative, decision table, decision tree.
6. External Unity
- A something, that is in external system, but it is giving a data to system or giving data from system.
- The symbol is notation box.
- External entity is not a part of system.
- Naming :
b. Terminal not have a same name, except the object in same.
7. Data Flow
- It is a place flowed the information
- Described the straight line that connects the components of the system
- Flow data is shown with the direction arrows and the name on the flow of data that flows
- Flow data flow between processes, data storage and data flow indicates that the form of data input for the system
- Guidelines of the name:
Name of the flow of data that consists of some words associated with the flow lines connect.
No flow data for the same and the name should reflect its content.
The flow of data that consists of several elements can be expressed with the group element.
Avoid using the word 'data' and 'information' to give a name to the flow of data.
Wherever possible the complete flow of data is written
Terms of others:
Name of the flow of data into a process may not be the same as the name of the data flow out of the process.
Data flow into or out of data storage does not need to be given a name if: Flow of data simple and easy to understand, Flow of data describing all the data items.
There can be no flow of data from the terminal to the data storage, or vice versa because the terminal is not part of the system, the relationship with the terminal data storage must be through a process.
8. .Process
A process is an activity or work done by the person, machine or a computer from the data that flow into the process to produce data that will flow out of the process. Guidelines of the process:
Name of the process consists of a verb and noun, which reflects the function of the process.
Do not use the process as part of the name of a bubble.
May not have some process that has the same name.
The process should 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.
10. Data Storage
- Data storage is a storage data's place in system.
- That symbol is a pair of parallel line or two line with one of side.
- Process can take data from or giving data to database.
- Director for gifting the name.
a. The name must reflect data storage.
b. If its name more than one word, so must giving continued sign.
10. DFD Symbol
11. Balancing in DFD
- Data flow which come into and out from a process must same with data flow which come into and out from detailed process in it's lower level.
- Name of the data flow which come into and out from process must have same name with name of data flow which come into and out from it's detailed process.
- Number and name of entity outside the process must same with name and outside entity from it's detailed process.
- The issues that must be considered in the DFD which have more than one level.
- Must have balance input and output between one level and next level.
- Balance between level 0 and level 1 seen in input or output from data flow go or from terminal in level 0, while balance between level 1 and level 2 seen in input or output from data flow go or from process concerned.
- Data flow name, data storage and terminal each level must same if the object same.
12. Prohibition in DFD
- Flow data may not be from outside the entity directly to other outside entities without going through a process.
- Flow data may not be from the savings directly to the data to outside entities without going through a process.
- Flow data may not be saving the data directly from the savings and other data without going through a process.
- Flow data from one process directly to the other without going through the process of saving data should / be avoided as much as possible.
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