DATA FLOW DIAGRAM
DFD is often used to develop a system or new system which developed logically without considering physical environment where data is streamed
DFD represent tool that used appliance at methodologies of structural system development
Data Flow Diagram
- Depicting the division of system into smaller module
- Facilitating user who has less knowledge about computer area to understand system which to be done.
Context Diagram
- Consist of one process and depict scope from a system
- Representing highest level of DFD which is depicting all of input to system and output form system
- System limited by boundary ( depicted by dash line)
- There may not be any is depository ( storage)
Zero Diagrams
- Depicting process of DFD
- Giving view by totally about system which is handled, showing existing especial process or function, data stream and of external entity
- At this level is enabled by the existence of data storage For process which is not detailed again in the next level so enhanced by symbol ‘*’ or ‘ P’ at the end of process number
- Balance of Input and output ( balancing) between diagram 0 with context diagram have to be looked after
Detailed Diagram
- Representing diagram which is elaborating the process which is in zero diagram or level above it
- In one level there are shall not more than 7 process and maximal 9, if more, then decompositions must be done
Process Specification
- Every process in DFD must have the specification of process
- At top level method that used to depict process can using descriptive sentence
- At more detailed level, at most under of process ( primitive functional) need more structural specification
- Specification of process will become guidance to programmer in making program ( coding )
- Method which is used in specification of process: breakdown of process in form of story, decision table , decision tree
External Unity
- Something that beyond of system, but it give data into system or give data from system
- Symbols by notation box
- External entity is not the part of system
- Naming:
· Name of terminal in form of noun
· Terminal may not have same name except its object are same object
Data Flow
- Representing place where is information is streaming
- Depicted with straight line which is connecting component of system
- Data flow shown with line and direction bow get named by data flow which is streaming
- Data flow streamed among process, data storage and show data flow from data which is in form input for system.
- Guidance of giving a name:
· Name of data stream which is consist of some stream word related by continued line
· There may not any data stream that its name are same and name that was given have to express its contents
· Data stream which is consist of some element can be expressed with group of element
· Avoid to use word ‘ data’ and ‘ information’ to give a name of data stream
· Laboring to data name of data stream completely written
- Other rule:
· Name of data stream which is come into a process may not equal with name of data stream which is out from it process
· data Flow which is into or go out from data of storage didn’t need be named when :
· Data stream is comprehended easy and simple
· Data stream depict all of data item
· There may not be any data stream from terminal to data storage or on the contrary because terminal isn’t part of system, relation between terminal with data storage have to through a process
Process
A process is activity or job by people, computer or machine from result of a data flow which enter into process.
- Process represent what is system done
- Process can processing data stream or data input to become output data stream
- Function of process are to transforming one or more data input to become one or more output data according to specification which is wanted
- Each process have one or some input and also yield one or some output
- Process often also called as bubble
- Guidance to giving process name:
· Name of process consist of noun and verb which is expressing function of that process
· Don’t use word “process” as part of the name of a bubble
· There are may not any some process which have same name
· Process has to numbered. Number sequence as possible follow process sequence or stream, but that way number sequence didn’t mean absolutely represent sequence of process chronology
Data Storage
- Data storage represent place to data repository in system
- A couple of parallel line or two line which is one side of it is openly is symbol of data storage
- Process can take data from or give data to database
- Guidance to giving name:
· Name have to express data storage
· When its name more than one word so have to addicting with continuous line
Data Dictionary
- Data Storage assist perpetrator of system to interpret application detailed and organizational all of data element which is used precisely by system so that user and system analyst have same idea about input, output, storage and process
- At analysis phase, data dictionary used as communication tool among system analyst and user
- At phase of scheming system, data dictionary used to designing input, database and report
- The character of data flow at DAD is global, more detailed information can be seen at data dictionary
- Data dictionary load the followings:
· Name of data flow: have to be noted so reader need more clarification about a data flow can look for it easily
· Alias: other name or alias of data can be written if it has
· Data form: used to grouping the data dictionary into its use when system scheming
· Data flow: showing where is data streaming from and where data to go
- Clarification: giving clarification about meaning of data flow
Balancing on DFD
- Data stream which come into and go out from one process have to equal to data stream which come into and go out from detail of process at level under it
- Name of data stream which come into and go out from one process have to equal to name of data stream which enter into and go out from detail of process
- Amount and name of external entities from a process have to equal to name and amount of external entities from detail of process
- Something which must be gave attention to DFD which is has more than one level:
- Input and output between one level and next level Have to balance
- The balance between level 0 and level 1 seen at input / output of data stream into or from terminal at level 0, while balance between level 1 and level 2 seen at input / output from data stream into / from pertinent process
- Name of data stream, data storage and terminal at every level have to be same if its object are same
Prohibition in DFD
- Data flow may not from directly external entity go to other external entity without passing a process
- Data flow may not from directly data deposit go to external entity without passing a process
- Data flow may not from directly data deposit go to the other data deposit without passing a process
- Data flow from one directly process goes to other process without passing data deposit may better as possible avoided.
