using data flow diagrams
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Using Data Flow Diagrams
Chapt
er 7
DATA Flow ApproachConceptualize:
“ how data move through the organization ““ the process or transformation that the data undergo “
“ and what are the outputs “
Data Flow Diagrams (DFDs)
ⱷ emphasize the processing of data or the transforming of data as they move through a variety of processes.
Advantages of the Data Flow Approach
Have 4 advantages1. Freedom from committing “technical
implementation of the system”
2. Further understanding of the interrelatedness of systems and subsystems.
3. Communicating current system knowledge to users
4. Analysis of a proposed system to determine if the necessary data and processes have been defined
Conventions used in DFDs
Developing data flow DiagramsDeveloping Data Flow DiagramsUsing a Top – Down Approach
1. Make a list of a business activities and use it to determine various External entities
Data flows Processes Data stores
2. Create a context diagram that shows external entities and data flow to and from the system. Do not show any detailed processes or data stores3. Draw diagram 0, the next level. Show processes, but keep them general. Show data stores at this level.4. Create a child diagram for each of the processes in Diagram 0.5. Check for errors and make sure that labels you assign to each processes and data flows are meaningful.6. Develop a physical data flow diagram from the logical data flow diagram. Distinguish between manual and automated processes, describe actual files and report by names and add controls to indicate when processes are complete or errors occur.7. Partition the physical data flow diagram by separating or grouping parts of the diagram in order to facilitate programming and implementation.
1st
Basic rules to follow:1. Must have at least one process.2. A process must receive at least one data flow
coming into process and leaving from the process.3. A data store should be connected to at least one
process.4. External entities should not be connected to each
other.
2nd Creating the context
diagram
0
SystemName
Input A
Input B
Output C
D1 Data Store 1 D1 Data Store 1
Entity3Entity
3Entity
2Entity2
Entity1Entity
1
3rd
Drawing Diagram 0
4
General Process
DDD
3
General Process
CCC
2
General Process
BBB
1
General Process
AAA
D1 Data Store 1 D1 Data Store 1 D2 Data Store 2 D2 Data Store 2
Entity1Entity
1
Entity2Entity
2
Entity3Entity
3
Data Flow C
Data Flow B
Record ERecord A
Record A Record E
Data Flow DInput B
Input A Output C
4th Creating Child Diagrams
4General Process
DDD
3General Process
CCC
D1 Data Store 1 D1 Data Store 1
Entity2Entity
2
Record A
Data Flow DInput B
3.2Detailed Process
YYY
D1 Data Store 1 D1 Data Store 1
Record A
TransactionRecord 1
3.2Detailed Process
ZZZ
Detailed Data Flow Z
Data Flow D
D5 transaction File 1 D5 transaction File 13.1
Detailed Process
YYY
TransactionRecord 1
Error
Input B
5th
Checking the Diagrams For Error
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