DATA FLOW DIAGRAM

What is a data flow diagram?

A data flow diagram (DFD) is a graphical description of the ebb and flow of data in a given context. DFD allows you to identify the transformations that take place on data as it moves from input to Output in the system. (DFDs pre-date UML diagrams, but still have a complementary role to play in describing systems.)

Developing a data-flow diagram

Top-Down Approach

1. The system designer makes “a context level DFD” or Level 0, which shows the “interaction” (data flows) between “the system” (represented by one process) and “the system environment” (represented by terminators).

2. The system is “decomposed in lower-level DFD (Level 1)” into a set of “processes, data stores, and the data flows between these processes and data stores”.

3. Each process is then decomposed into an “even-lower-level diagram containing its subprocesses”.

4. This approach “then continues on the subsequent subprocesses”, until a necessary and sufficient level of detail is reached which is called the primitive process (aka chewable in one bite).

DFD is also a virtually designable diagram that technically or diagrammatically describes the inflow and outflow of data or information that is provided by the external entity.

Event Partitioning Approach

Event partitioning was described by Edward Yourdon in Just Enough Structured Analysis.^[4]

1. Construct detailed data-flow diagram.

1. The list of all events is made.

2. For each event a process is constructed.

3. Each process is linked (with incoming data flows) directly with other processes or via data stores, so that it has enough information to respond to a given event.

4. The reaction of each process to a given event is modeled by an outgoing data flow.

Data Flow Diagram (DFD)

- Describes the distribution of the system in to a smaller modules

- Easier for users with less understanding field of computer to understand the systems that will be done

Context Diagram

- Consists of a process and describe the scope of a system

- Is the highest level of the DFD that describes the entire of input in to system and output of the system

- System is limited by Boundary (depicted by broken lines)

- No storage

Zero Diagram

- Describes the process of the DFD

- Providing views on the overall system in which, showing the main process or function, the flow of data and entity external

- At this level of data storage possible

- To process that does not be detailed again on the next level then added to the symbol ‘*’ or ‘P’ at the end of the process

- Balance of input and output (balancing) between zero diagram with context diagram should be maintained

Detailed Diagram

- Is the diagrams that decompose a process that is in the diagram zero or level above

- Numbering level in the DFD:

1. Level Name : 0, Diagram Name : Context, Number of process : -

2. Level Name : 1, Diagram Name : Diagram 0, Number of process : 1.0, 2.0, 3.0, …

3. Level Name : 2, Diagram Name : Diagram 1.0, Number of process : 1.1, 1.2, 1.3, …

4. Level Name : 3, Diagram Name : Diagram 1.1, Number of process : 1.1.1, 1.1.2, …

- In one level there should be no more than 7 units and the maximum of 9, when more should be done in the decomposition

SPECIFICATION PROCESS

- Each of process in the DFD must have a specification process

- At the top level method is used to describe the process can use by a descriptive sentence

- At a level more detailed, namely on the process bottom (functional primitive) requires specification of a more structured

- Specification process will be the guideline for the programmer to make this program (coding)
Method used in the specification process : the process of disintegration in the form of a story, decision table, decision tree

ON FOREIGN

- Something that is outside the system, but it provides data in the system or to provide data from the system

- The symbol with the notation box

- External entity not part of the system including

- Naming:

1. The name of the terminal are noun

2. Terminal may not have the same name except the object are same

CASH DATA

- Is the place flow of information

- Depicted with the straight line that connects the components of the system

- Data flow direction is indicated with arrows and lines give the name on the flow of data that flows

Flow data flows between processes, data storage and indicates data flow form of data input for the system

- Guidelines of the naming:

1. Name of the flow of data that consists of some words associated with the flow lines connect

2. No flow data for the same and the name should reflect its content

3. The 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

- Other provisions:

1. 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

2. Data flow into or out of data storage does not need to be given a name if:

§ The flow of data simple and easy to understand

§ Describes the data flow of all 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

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

- Transform the process of working one or more of the input data 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 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

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

STORAGE DATA

- Data storage is a storage place for data that exists in the system

- Symbol 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 of the name:

1. The name should reflect the data storage

2. When his name more than one word must be marked with the number

DATA DICTIONARY

- 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 process

- At analysis, the data dictionary is used as a means of communication between the systems analyst with the users

- At the system design, 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

5. Description: to give an explanation of the meaning of the data flow

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

- Name of the data flow into and out of the process must match the name of the flow of data into and out of the details of the process

- Number and the name of an entity outside the process must be equal to the number of names and entities outside 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 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. 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

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