DFD is a logical data model or process that is made to describe the origin of the data and the destination where the data out of the system, where data is stored, the process that produces the data and the interaction between the data stored and the process is imposed on data.
DFD are often used to describe a system that already exists or the new system will be developed logically without considering the physical environment where the data flows, or where data are stored.
DFD is a tool that is used in the system development methodology is structured. Excess primary data flow approach, namely:
1. Freedom from the implementation of technical systems.
2. Understanding more about the relation to one another in the system and subsystem.
3. Communicate knowledge of the system with the user through the data flow diagram.
4. Analyzing the proposed system to determine whether the data and processes required are defined.
Besides, there are additional advantages, namely:
1. Can be used as a useful exercise for analyst, so it can better understand the relation to one another in the system and subsystem.
2. Differentiate the system from the environment by placing boundaries.
3. Can be used as a device to interact with users.
4. Allows analyst describe each component used in the diagram.
Type the first Context diagram, data flow diagram is the top level (Top Level DFD), the diagram is not the most detail, from an information system that describes the stream-flow data in and outside the system and to the outside and to external entities. (CD describes the system in a loop and relationships with outside entities. Circle shows that the overall process in the system).
Some of the things that must be considered in drawing a CD:
· * Terminology system:
· – Delivery System is a line between “the interests of the system”.
· – Environmental System is all things that relate or affect the system.
· – Interface is the flow of a system that connects with a circle system.
· * Using a symbol of the process,
The entry in the context of the circle (the symbol) is an activity information processing (Delivery System). Activity is taking information from the data file, transform data, or doing filing data, such as preparing documents, enter, check, classifying, organize, sort, calculate, summarize data, perform filing and data (either manually or do that would be conducted terotomasi ).
· * The name / description of symbols in the process according to the functions of the system.
· * Between External Entity / Terminator is not allowed direct communication
· * If there are terminator that have many inputs and outputs, are described for more than one so that to prevent the drawing is too complex, with a sign asterisk (*) or cross-line (#).
· * If the Terminator represents individuals (personnel) should be represented by the role that these ridiculed personnel.
· * Flow of data to process and output information as the outgoing flow of data is different.
· Describe the process of the DFD
· Provide views on the overall system in which, showing the main function or process that is, the flow of data and entity sterna
· At this level of data storage possible
· For processes that do not specified again on the next level then added the symbol ‘*’ or ‘P’ at the end of the process
· input and output balance (balancing) between 0 to diagram context diagram should be maintained
- It is a process diagram that decipher what is in the diagram zero level or above
- numbering level in the DFD:
- In the one level there should be no more than 7 units and the maximum of 9, when more should be done in the decomposition
• Each process in the DFD must have a specification process
• At the top level method is used to describe the process can use a sentence with descriptive
• On a more detailed level, namely on the bottom (functional primitive) requires specification of a more structured
• specification process will be the guideline for the programmer to make this program (coding)
• Methods used in the specification process: the process of disintegration in the form of a story, decision table, decision tree
• Something that is outside the system, but it provides data in the system or to provide data from the system
• Symbolized with the notation
• External entity not part of the system including
· The name of the form of noun
· Terminal may not have the same name except the object same
• It is a place to flow 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 is the same name and the name should reflect its content
• 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
• the extent possible the flow of data is complete
• 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 describes all data items
· No flow 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
• 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:
§ 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
§ There may be 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
- 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 of the side open, process can retrieve data from or provide data to the database
- Guidelines of the name:
§ The name should reflect the data storage
§ If the name more than one word must be marked with the number
- 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
- At the analysis stage, the data dictionary is used as a means of communication between the systems analyst with the
- 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:
- Name of the 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
- The form 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: provides an explanation about the meaning of the data flow
Sample data dictionary:
BALANCING IN THE DFD
- 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 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:
- There should be a balance between input and output of one level and next level
- 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
- Name of the flow of data, data storage and terminals at each level must be the same if the object same
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 of data from one process directly to the other without going through the process of saving data should / be avoided as much as possible
NGURAH AGUS SANJAYA ER, S.KOM, M.KOM, Slide Persentation DFD
Pengembangan Sistem Informasi, 1998. Leman, PT Elex Media Komputindo, Jakarta
Pengantar Sistem Informasi Bisnis, 1995. Lani Sidarta, PT Elex Media Komputindo, Jakarta