(DFDs)(DFDs)
Data Flow Diagrams (DFDs)Data Flow Diagrams (DFDs)
 
Sarson)Sarson)
Process
!or" or actions perormed on data (inside the system)
 
$ule % rocess$ule % rocess
 
 
 
Data StoreData Store
*s used in a DFD to represent data that the system stores
#abels should be noun phrases
 
$ule Data Store$ule Data Store
 
SourceSin" (-xternal -ntity)SourceSin" (-xternal -ntity)
-xternal entity that is origin or destination o data (outside the system)
*s the singular orm o a department. outside organisation. other *S. or person
#abels should be noun phrases
Source – Entity that supplies data to the
system
system
 
Data Flow 0hat 'onnects  YES NO
A process to another process
A process to an external entity
A process to a data store
An external entity to another external entity
An external entity to a data store
A data store to another data store
 
 0op1level view o *S
Shows the system boundaries. external entities that interact with the system. and ma2or inormation fows between entities and the system3
 
#evel16 DFD#evel16 DFD
Shows the system5s ma2or processes. data fows. and data stores at a high level o abstraction
 
Functional Decomposition 7n iterative process o brea"ing a system
description down into 8ner and 8ner detail
/ses a series o increasingly detailed DFDs to describe an *S
9alancing  0he conservation o inputs and outputs to
a data fow process when that process is decomposed to a lower level
 
DFDsDFDs  0op1down strategy
'reate the high1level diagrams ('ontext Diagram). then low1level diagrams (#evel16 diagram). and so on
9ottom1up strategy
 
-xercise recision 0ools sells a line o high1:uality woodwor"ing tools3 !hen customers place orders on the company5s !eb site. the system chec"s to see i the items are in stoc". issues a status message to the customer. and generates a shipping order to the warehouse. which 8lls the order3 !hen the order is shipped. the customer is billed3 0he system also produces various reports3
 Draw a context diagram or the order system
 Draw DFD diagram 6 or the order system
 
*dentiy -ntities.rocess.Data Stores & Data*dentiy -ntities.rocess.Data Stores & Data -ntities
'ustomer
!arehouse
7ccounting
rocesses