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 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).
There is even symbol Data Flow Diagrams:
1. External Entity
2. Process
3. Data flow
4. Data Storage
CONTEXT DIAGRAM
System Context Diagram are diagrams used in systems design to represent all external entities that may interact with a system. This diagram pictures the system at the center, with no details of its interior structure, surrounding by all its interacting systems, environment and activities. The objective of a system context diagram is to focus attention on external factors and events that should be considered in developing a complete set of system requirements and constraints.
Context diagrams are used early in a project to get agreement on the scope under investigation. Context diagrams are typically included in a requirements document. These diagrams must be read by all project stakeholders and thus should be written in plain language, so the stakeholders can understand items within the document.
ZERO DIAGRAM
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.
DETAIL DIAGRAM
• Detail Diagram is a Diagram to describe process in zero diagram or high level.
• In one advisable level has no is more than 7 processes and maximal 9, if more therefore has to be done by decomposition
SPECIFICATION OF PROCESS
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 At 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). Method used in the specification process: the process of disintegration in the form of a story, decision table, decision tree
SYMBOL in DFD:
1. External entity
2. Data Flow
3. Process
4. Data Store
A. EXTERNAL ENTITY
Something in outside system, but its give data into system or give data for system, symbol with a notation box. External entity not include of part system. one that included outer unity amongst those:
1. An office, department or division in corporate but system open air, which is developed.
2. Person or a group person at organization but outside sys tem which being developed.
3. An organization or person of outside organization as e.g. subscription, provider.
4. Outdoor other information system, system being developed.
5. Original source of a transactions
B.DATA FLOW
Symbol with the dart, where is data flow is flow between process, data trove.. Data flow symbol with straight line to connective component of system. Data flow direction is indicated with arrows and lines give 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.
Guide of Data Flow name:
• Name of data flow which consist of some word flow attributed with continued line.
• There may not be any data flow which its same name and gift of name have to express its contents
• Data stream which consist of some element can be expressed with element grup
C.PROCESS
Process is activity or job that did by person, machine or computer of result a data flow that turns in at to process to been resulted data flow that will come out from process. Function of process is transformation one or some input data become one or some output data as according to specification. Each process have one or some input and also result one or some output data. Frequent process may be called by bubble. Symbols used : circle
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.
D.DATA STORAGE
Data store is storage place for data that exists in the system. Data store symbol with couple two parallel line or two line wrongly one side from other side openly.
The process can retrieve data from or provide data to the database as follow:
1. file or database in the computer system
2. manual record keeping or
3. the data in a table
4. table reference manual
5. agenda book
Guide of Data Store name:
• The name should reflect the data storage
• When his name more than one word must be marked with the number
Dictionary of Data (Catalog Data)
Is a catalog (storage) of the elements that are in a system. Data dictionary is also called with a system data dictionary is a catalog of facts and data information needs of an information system. In function to help system agent to interpreting application in detail and organization all of data element that utilized by system exactly so user and system analyst have same understanding basic about entry, output, storage and process.
On analysis stage, data dictionary constitute communication device among user and system analyst about data which is flow in system, which is about in going data to system and about information which needed by user. In the meantime, on lexical system scheme stage data is utilized to design input, reporting and database. Data flow in DFD have the character of globally, boldness more detailed can be seen in data dictionary.
Data dictionary load the followings :
• Name of data current: 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
Balancing In DFD
Data flow 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. 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. We must be considered in the DFD which have more than one level:
• Shall available input balance and output among one level and next level
• Balance among level 0 and level 1 is seen on input / output of data flow goes to or of terminal on level 0, meanwhile balance among level 1 and level 2 are seen on input / output of data flow goes to / of process that pertinent
• Data streaming name, storage data and terminal on every level shall same object.
Prohibition in DFD
• Data flow may not from external entity directly to wend another external entity without passing a process.
• Data flow may not from direct data deposit go to external entity without passing a process
• Data flow may not from direct data deposit go to other data deposit without passing a process
• Data flow from one direct process go to other process without passing a data deposit better possible avoided.
References:
• ER Ngurah Agus Sanjaya, S.KOM, M.KOM. Slide Part 4 - DATA FLOW DIAGRAM.
• HM, Jogiyanto. 2005. Analisis & Desain Sistem Informasi. Yogyakarta: ANDI.
• http://id.wikipedia.org/wiki/Data_flow_diagram
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