DATA FLOW DIAGRAM

To facilitate depiction of a system or the new system will be developed without considering the logic of the physical environment where the data flow or the physical environment where the data is saved, then we use the Data Flow Diagram (DFD). DFD is a tool that can describe the flow of data in a system with a structured and clear, that is why DAD is a tool the most important for a systems analyst. DAD can represent a system that automatically or manually by using the image in the network graph.

DFD consists of a context diagram and a detailed diagram (DFD Levelled). Context diagram map model work environment (describing the relationship between external entities, input and output system), which is represented with a single circle which represents the overall system. System is limited by Boundary (depicted by broken line), and at the time of presentment may not have storage (storage).

DFD describes the system as levelled networks between functions related to one another with the flow and storage of data, this model only makes the model system from the point of view function.

DFD will be levelled in a decline in the level where a decrease in the lower level must be able to represent the process in a clear specification of the process. So levelled in DFD can be started from the DFD level 0 and then go down to the DFD level 1 onwards. Each reduction is done only when necessary. The flow of incoming data and exit the process at a level x must be related to the flow of incoming data and exit the level x +1 in the process of defining the level of x is. Process that can not be revealed / told dirinci more primitive functional and the process referred to as primitive.

Each process in the DFD must have a specification process. At the top level method is used to describe the process you can use with descriptive sentences. At a more detailed level, namely on the bottom (functional primitive) require a more structured specification. 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.

TERMINATOR COMPONENTS / FOREIGN ENTITY
Terminator represent external entities that communicate with the system that is currently being developed. Terminator usually known by the name of foreign entities (external entity).
There are two types of terminator:
1. Terminator Source (source): the terminator of a source.
2. Terminator Destination (sink) is the terminator that was the purpose of data / information system.

Terminator can be a person, group of people, organizations, departments within the organization, or the same company but outside the control system that is being made models.

Terminator can also be departments, divisions or systems outside the system that communicate with the system that is currently being developed.

Terminator components need to be given this name in accordance with the outside world that communicate with the system that is being made model, and usually use the noun, for example, Sales Section, Lecturer, Student.

There are three important issues that must be remembered about the terminator: Terminator is a part / the environment outside the system. Data flow that connects terminator system with different processes, the system shows the relationship with the outside world. Professional Systems reserve the right not to change the contents or the way work organization or procedures relating to the terminator. Relationship existing between the terminator with each other is not described in the DFD.

DATA FLOW

Is the place mengalirnya 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 flow. Flow data flow between processes, data storage and data flow indicates that the form of data input for the system

* Guidelines of the name:
0 Name of the flow of data that consists of some words associated with the flow lines connect
0 No flow data for the same and the name should reflect its content
0 The flow of data that consists of several elements can be expressed with the group element
0 Avoid using the word 'data' and 'information' to give a name to the flow of data
0 Wherever possible the complete flow of data is written

* Other provisions
0 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
0 Data flow into or out of data storage does not need to be given a name when the flow of data simple and easy to understand and describe the data flow of all data items
0 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
Describe the process components of the system that transform input into output. The process is given a name to describe the process / activities that are / will be implemented. Giving the name of the process is done by using the transitive verb (the verb requires an object), such as Calculating Salaries, Printing KRS, Calculating Number of SKS. There are four possibilities that can occur in the process with respect to input and output:

There are a few things to note about the process:

0 The process must have input and output.
0 The process can be connected with the terminator component, process or store data through the data flow.
System / section / division / department that is being analyzed by the professional system with the described process components.

Here is wrong example of a process:

Generally, errors in the DFD process is:

1. The process does not have any input but the output. This error is called the black hole (black hole), because the data into the process and disappeared like to include in the black hole (see process 1).

2. The process of producing output, but did not receive input. This error is called a miracle (magic), because the output produced magically without ever receiving input (see process 2).


COMPONENT DATA STORE
This component is used to create a model set of data packets and given the name of the plural noun, such as Student. Data store is usually associated with the storage-storage, such as file or database associated with an in-store computer, such as a diskette file, files, hard disk, magnetic tape files. Also store data related to the storage manually, such as address books, file folders, and agenda.

A data store associated with the flow of data only on the component processes, not with the other components DFD. Data flows that connect the data store with an understanding of the process have the following:

Flow data from the data store, which means as the initialization or reading one single packet of data, more than one packet of data, part of a single packet of data, or part of more than one data packet to a process (see figure 2 (a)).

Flow of data to store data, which means as data updates, such as adding a new data packet or more, remove one or more packages, or change / modify one or more data packet (see figure 2 (b)).

In the first data store does not change, if a packet of data / information from a data store to a process. Instead of the second data store has changed as a result of the flow enters the data store. In other words, the process flow of data is responsible for the changes that occur in the data store.

DFD SYMBOLS

DICTIONARY OF DATA (CATALOG DATA)

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 the systems analyst with the user. At the system design, data dictionary is used to design input, reports and databases.

* Load the data dictionary as follows:
0 Name of data flow: must note that readers who need further explanation about a flow of data can find it easily
0 Alias: the name of the data can be written when there is
0 Forms of data: used to segment the data dictionary to use when designing the system
0 Flow data: indicates from which data flows and where the data
0 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:
0 There must be a balance between input and output of one level and next level
0 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
0 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