Data Flow Diagram

Data flow diagram

A data-flow diagram (DFD) is a graphical representation of the "flow" of data through an information system. It differs from the flowchart as it shows the data flow instead of the control flow of the program.

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). Expresed system into smaller modul and help user, which less comprehending in computer science to understand with a system, which to work it

Context Diagram
Context Diagram is :
-> include one process and expressed scope from a system
-> it's the highest level from DFD which expresed all input into the system and output from system
-> sytem is bounded by the boundary (it's shown by the dashed line)
-> there isn't any storage

Zero Diagram
-> showing the process of DFD
-> giving totally opinion about the system which is handle it, showing the prime funtion or process, data flow and eksternal entity
-> in this level, are possible to data storage
-> for process which isn't eksplained in next level, enhanced symbol "*" or "P" at the end of the process number
-> balancing input and output between zero diagram and context diagram have to maintained

Detailed Diagram
-> is the diagram which explain what process are in the zero diagram or higer level
-> nubering level on DFD:
-> in the same level, is better if there aren't more than 7 process and maximum 9 process, if more then it must be dekomposize

Process Specification
-> every process in DFD must have specification
-> in top level, used method to express process may use descriptive sentence
-> in the detailed process that is the most under process (functional primitive) need more structural specification
-> the process specification will become guidance to programmer to coding
-> used method to process specification:
-> description process in story form
-> decision table
-> decision tree

Outer Unity
-> something is outside system, but it giving input into system or giving data form system
-> symbolized with box notation
-> external entity isn't part of system
-> naming :
-> terminal's name is noun form
-> terminal's name must be diferrent, except the object is same

Data Flow
Data flow is a Place for information stream. 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
->Avoid usage of word ‘ data’ and ‘ information’ to give the name at data flow
->As possible the name of data flow written is complete

Other rule:
->Data flow name which turn in at a process may not same by the name of secretary data flow of that process.
->Data flow into or out of data storage doesn't need to give a name if:
->The flow of data simple and easy to understand
->Describes the data flow of all data items
->There may not any data flow of terminal to data storage or on the contrary because terminal isn't part of system, terminal relation with data storage have to pass process.

Process
-> process is what is done by system
-> process could processing data or flowing data input to flowing data output
-> function of process is transforming one or several data input into one or several data output which according to spcification is needed
-> every process has one or several input and produce one or several output
-> process is also called bubble

guidance for naming process :
-> name of process include verb and noun which expressing the function of that process
-> don't use word "process" to a part of naming bubble
-> there aren't some process which same name
-> process have to give numbered. order of number must possible following the flow or order process, but an ordered number of process is not absolut expressing the ordered process chronologically

Data Storage
-> data storage is a place to saving data which existing in system
-> symbolized with a set of a row lines or two lines whith one side opened
-> process can taking data from or giving data to database
-> guidance for giving name :
-> name must expressed data storage
-> if the name include more than one word, then must given continued sign

DFD Symbol


Dictionary Data
-> function to help perpetrator of system to interpreting application detailly and organized all data element which used by system until user and system analsyt have same concept about input, output, storage and process.
-> in analysis phase, dictionary data is used as communication tolls between system analyst and user
-> in planning phase of the system, dictionary data is use for planning input, report and database
-> data flow in DAD is global

Dictionary data is substance of case bellow :
-> name of data flow : have to be noted in order that reader which need next explanation about a flown data can be search easily
-> alias : other name of data, could writen if it has
-> data form : used to clasified dictionary data to it's uses when planning the system
-> data flow : showing from where data is coming and where data is going
-> explanation :giving explanation about the meaning of data flow

Balancing in DFD
-> data flow which come into and out from a process must same with data flow which come into and out from detailed process in it's lower level
-> name of the data flow which come into and out from process must have same name with name of data flow which come into and out from it's detailed process
-> number and name of entity outside the process must same with name and outside entity from it's detailed process
-> The issues that must be considered in the DFD which have more than one level
-> Must have balance input and output between one level and next level.
-> Balance between level 0 and level 1 seen in input or output from data flow go or from terminal in level 0, while balance between level 1 and level 2 seen in input or output from data flow go or from process concerned.
-> Data flow name, data storage and terminal each level must same if the object same.

Prohibition order in DFD
-> Data flow may not from external entity direct to external entity without through a process.
-> Data flow may not from data storage direct to external entity without through a process.
-> Data flow may not from data storage direct to other data storage without through a process.
-> Data flow from one process direct to other process without through a saving data should or be avoided as much as possible.

Reference:
Agus Sanjaya ER, S.Kom, M.Kom ,presentation slide : Diagram Aliran Data