Part 4 - DATA FLOW DIAGRAM

DATA FLOW DIAGRAM (DFD)

• Figuring system division into smaller module
• Facilitate user that insufficiently understand about computer area to understands system that will be worked

CONTEXT DIAGRAM

• Consist of one process and figures scope of a system.
• Constituting supreme level from DFD that figure all of input and output of system.
• System limited by boundary (figured by dotted line)
• Stored is may not there

ZERO DIAGRAMS

• Figuring the process of DFD
• Giving view thoroughly hit handled system, pointing out function or aught main process, data flow and external entity
• This level is enabled existence of data storage
• For the process that do not elaborated again on succeeding level, then increased *' or P' symbol at the end of process numbers
• Balance of input and output between zero diagram and context diagram should be maintained

DIAGRAM DETAILED

Diagram detail is diagram that describes what the process that available in zero diagram or level on it.
Numbering level of DFD:







In one level is better has no more than seven processes and maximal processes are nine, if it has more then has to done the decomposition.

SPECIFICATION PROCESSES

• Each process on DFD should have process specification.
• On top level, method that used to figure the process is by use descriptive sentence
• On more detail level which on lower process (functional primitive) need the specification that more structured.
• Specification process will be guidance for the programmer in makes program (coding)
• Method that used in specification process: Breakdown of process in shaped story, decision table, and decision tree.
  

EXTERNAL ENTITY

• Something that lie at beyond of the system, but it gives data into the system or gives data of system.
• Symbolized with notation box
• External entity excluding the part of system
• Naming:

1.Terminal name is substantive as.
2.Terminal may not have same name except the object is same.


DATA FLOW

• Data flow is a place to make a flow information.
• Figured by straight line that linking the component of system
• Data Flow is pointed out with arrow and line is named by data flow that is steaming.
• Data flow is streaming among the process, data storage and shows the data flow of data that form the input for the system.

Name Application guidance:

• Data flow’s name which consists from several word streams is linked by connected line.
• No data flow that have name equality and name application shall reflect its content.
• Data flow that consisting of many elements gets to be declared for by element group.
• Avoid employing word “data” and “information” if we want to give name of data flow.
• As much as can data flow name is written completely

Other Rule:

• Data flow’s name that turns in at a process may not same by the name of data flow that turns out from the process.
• Data flow that turn in at a data storage or turns out from data storage not necessarily been given name, if:
• Data flow are simple and comprehensible
• Data flow figures all of data item
• No data flow from terminal to data storage or in the contras, because terminal is not part of system, terminal relationship with data storage shall pass through the process.

PROCESS

• Process constitutes what the system done.
• Process can process data or input data flow become output data flow.
• Process has a function to transform one or many input data become one or many output data appropriate to specification that needed.
• Each process has one or many input and resulting one or many output
• Often process is called bubble

Guidance of Process Naming

• Name of processes consisting of verb and noun that reflect that process function.
• Don't use "process" word as part of name a bubble.
• May not there many process that have same name
• Process should be numbered. Number thread as much as can follow the flow or process thread, but thus number thread doesn't mean absolutely constitute chronologically process thread.

DATA STORAGE

• Data storage aught data repository in system
• Epitomized by a couple of equal line or two lines with single-sided sideways exposed.
• Process can take data of or gives data to the database.
• Name application guidance:
• Name shall reflect the data storage
• If its name more than one word then has to be hyphened

DATA DICTIONARY

Data dictionary have function in helping system user to interpret application in detail and organize all of data element that utilized by the system exactly until user and system analyst have same interpretation about input, output, storage and process.
When analysis phase, data dictionary is used as communication device between system analysts. Meanwhile at the system scheme phase, data dictionary is used to design input, report and database.
Data flow on DAD has global character and more detail information one can be seen on data dictionary.
Data dictionary is containing these things:

• Name of data flow: have to record to make reader that requires more explanation about a data current can look for it easily.
• Alias: alias or besides name of data can be written if available
• Data form: It used for clustering data dictionary into its purpose in time of design system.
• Data Flow: point out of which data is streaming and where its aim.
• Explanation: giving explanation about meaning of data flow.

BALANCING IN DFD

• Data flow that turns in at and turn out from one process have to equal with data flow that turns in at and turn out from details of process on level under it.
• Data flow's name which turn in at and turn out from one process have to same with the name of data flow that turns in at and turn out from details of that process.
• Total and name of extern entities of a process has to equal with total and name of extern entities of details of that process.
• Things who shall be noticed on DFD who between one level and the next level.
• Shall available balancing input and output between one level and next level.
• Balance between level 0 and level 1 is seen on input / output of data flow goes to or goes out from terminal on level 0, meanwhile balance between level 1 and level 2 are seen on input / output of data flow goes to / or goes out from process that pertinent.
• Name of data flow, data storage and terminal at every level should be same.

INTERDICTION IN DFD

• Data flow may not from extern entity directly to another extern entity without through a process.
• Data flow may not from data storage directly to another extern entity without through a process.
• Data flow may not from data storage directly to another data storage without through a process.
• Data flow from one process directly to the other process without going through the process of data storage should be avoided.

The SYMBOL use in DFD