Data flow diagram

Initiation

Development

Implementation

Operation and Maintenance

4 phases of an information system

Process

• transform inputs into outputs

• represented by a rounded box

• Describe as:

  • select

  • purchase

  • calculate

  • decide

  • adjust

  • hire

  • update

• Represent either:

  • A whole system

  • A subsystem

  • Work being done, an activity

• Names should be in the form verb-adjective-noun

  • The exception is a process that represents an entire system or subsystem

Data Flow

• movement of data between:

  • processes

  • data stores

  • external entities

• represented as arrows

• data identified along the arrow

• Shows the data about a person, place, or thing that moves through the system

• Names should be a noun that describes the data moving through the system

• Arrowhead indicates the flow direction

• Use double headed-arrows

  • only when a process is reading data and updating the data on the same table or file

Data Store

• location where data is stored

• it can be:

  • file cabinet

  • diskette

  • hard disk

  • answering machine and etc

• “where is the data?”

• open rectangle

• Name with a noun, describing the data

• (answer) are usually given a unique reference number, such as D1, D2, D3

• Include any data stored, such as:

  • A computer file or database

  • A transaction file

  • A set of tables

  • A manual file of records

External Entity

• any person or organization that provided data to a process in the system or receives data from a process

• square

• Represent people or organizations outside of the system being studied

• Shows the initial source and final recipient of data and information

• Should be named with a noun, describing that entity

Context Level Data Flow Diagram

• top-level data flow

• Contains only one process, representing the entire system

• The process is given the number zero

• All external entities are shown on the context diagram as well as major data flow to and from them

• The  diagram does not contain any data stores

Diagram 0

• is the explosion of the context level diagram

• Should include up to 7 or 9 processes

  • Any more will result in a cluttered diagram

• Processes are numbered with an integer

• The major data stores and all external entities are included on (answer)

Child Diagram

• A lower-level diagram may contain data stores not shown on the parent process, such as

  • A file containing a table of information (such as a tax table)

  • A file linking two processes on the child diagram

• Minor data flow, such as an error line, may be included on a (answer)

• Each process is numbered with the parent diagram number, a period, and a unique (answer) number

• Examples are:

  • 3.2 on Diagram 3, the (answer) 3

  • 5.2.7 on Diagram 5.2, (answer) 5.2

  • On Diagram 3, the processes would be numbered 3.1, 3.2, 3.3 and so on

Black Hole

• no output

• not valid

Spontaneous Process

• no input

  • not valid

Gray Hole

• mali yung input or output

• not valid