Data Flow Diagram
Data flow diagram
Data Flow Diagram (DFD) is a graphic illustration of the system that uses a number of forms of symbols to describe how data flows through a process of inter-related. DFD can be a program with the algorithm using circle and arrow symbol to represent the flow of data in the design program. The use of notation in the data flow diagram is very helpful to understand a system. DFD will help the user understand the missing field to understand the computer system that will be done because DFD describes the flow of data in the system with a structured and clear.
Some symbols used in the DFD to represent:
1. External entity
2. Data Flow
3. Process
4. Data Storage
Context Diagram
- The diagram which consists of a process and illustrate the range of a system.
- The highest level of the DFD that describes the entire system to input and output of the system
- System is limited by boundary
- There is No storage
Zero Diagram
- Diagram illustrating the process of the DFD. Giving view on the whole of system in which, showing the main function or process the flow of data and external entity.
- At this level of data storage is possible.
- To process in depth no longer on the next level then added the symbol ‘*’ or ‘P’ at the end of the process.
- Input and output balance between 0 to diagram context, diagram should be maintained.
Detailed Diagram
Is a diagram that interpret what is the process in the diagram zero level or above. On this diagram, a clarification of the process above will be done in a play. In one level there should be less than 7 units and the maximum of 9, when more should be done in the disintegration.
Numbering of level at DFD:
| Level Name | Diagram Name | Number of Process |
|
0 |
Context | |
|
1 |
Diagram 0 | 1.0, 2.0, 3.0, … |
|
2 |
Diagram 1.0 | 1.1, 1.2, 1.3, … |
|
3 |
Diagram 1.1 | 1.1.1, 1.1.2, … |
Specification process
Each process in the DFD must have a specification of the process, to explain the functioning of the process is in our system, the specification method used is the process of disintegration in the form of a sentence describe, decision table, decision tree. This specification will be a programmer for coding rule, because in this specification clearly visible flow process, and steps in each process. At the top level method is used to describe the process can use a sentence with descriptive and in a more detailed level, namely on the bottom (functional primitive) require a more structured specification.
Cash Data
Data flow in DFD is given an arrow symbol. This data flow indicates flow of data from the data that can be input to the system or the results of the processing system.
- Flow data consist of a group of related data elements in a logical move from one process to another process.
- Depicted with a straight line connecting the components of the system.
- Flow data is shown with the direction arrows and the name on the flow of data that flows.
- Cash flow of data between processes, saving data, the unit outside, and shows data flow from data in the form of inputs to 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
- 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:
7.1. The flow of data simple and easy to understand
7.2. Data flow describe the entire data item
- 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
Process
- The process is what is done by the system
- The process 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
- Each process has one or more inputs and produce one or more output
- The process is also often called bubble
- Guidelines of the process:
1. Name of 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. May not have some process that has the same name
4. 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
DFD Symbols
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Data Storage
Savings is a savings of data from the data can be:
a. Database file
b. Archive
c. Table
Here, a process can take data from the savings of this data. explained with a pair of parallel lines or two lines with one of the side open.
Guidelines of the name:
1. Name should reflect the data storage
2. When his name more than one word must be marked with the number
Data Dictionary
Working 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 and have a basic understanding of the same input, output, storage and process
1) At the analysis stage, the data dictionary is used as a means of communication between the systems analyst with the
2) At the system design, data dictionary is used to design input, reports and databases
3) Flow data on the global DAD, further details can be seen in the data dictionary
4) load the data dictionary as follows:
- Name of data flow: must note that readers who need further explanation about a flow of data can find it easily
- Alias: alias or other name of the data can be written when there is
- Forms of data: used to segment the data dictionary to use when designing the system
- Flow data: indicates from which data flows and where the data
Description: to give an explanation of the meaning of the data flow
Database
Work 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 and have a basic understanding of the same input, output, storage and processing. At analysis, the data dictionary is used as a means of communication between system analysts and users with the system design phase, the data dictionary is used to design input, reports and databases. Flow data on the global DAD, further details can be seen in the data dictionary
Load the data dictionary as follows:
1. Name of data flow: must note 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 there is
3. Forms of data: used to segment the data dictionary to use when designing the system
4. Flow data: indicates from which data flows and where the data
Balancing In DFD
The 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 it. This is not to be confusion in the process of the program, and the flow of data in accordance with the structure. Name of the flow of a process, must match the name of the details of the process flow diagram in the lower, the number and the name of an entity outside of the process, must be the same as the number and the name of the details of the process.
The issues that must be considered in the DFD which have more than one level:
1. There must be a balance between input and output of one level and the next level. Do not until the input and output level of 0 does not exist in the level 1.
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 or output of stream data to / from the process concerned
3. Name of the flow of data, data storage and terminals at each level must be the same if the same object
Restrictions 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
