1. Data Flow Diagrams – 3marks

Question 1

A data flow diagram (DFD) is…

Answer 1

A graphical analysis tool for structuring the requirements of an information system

Question 2

What does a DFD do?

Answer 2

A DFD identifies processes (programs, people or machines) that transform data when data flows through.

Question 3

What DOESN’T a DFD do?

Answer 3

Database design is not considered in DFDs

focus only on how inputs are converted into required outputs

Question 4

Why use a DFD?

Answer 4

Sometimes difficult and not necessary to provide a complete representation of the existing or future real system.

Question 5

A terminator is….

Answer 5

An external source/sink of information

Eg: the external entities of customer or manager.

Question 6

A terminator on a DFD is shown as…

Answer 6

A noun in a rectangle.

Question 7

A process is…

Answer 7

An activity that can occur in the information system

Eg: transform, generate, retrieve, delete data

Question 8

On a DFD a process must have…

Answer 8

Both incoming and outgoing dataflows (one or more)

Question 9

A process on a DFD is shown as…

Answer 9

An active verb inside a rectangle with rounded edges and a ruled section across the top with the ID.

Question 10

A data flow is represented on a DFD with the criteria….

Answer 10

A noun-labelled (data name) arrow which must go to or from a process

Question 11

A data store is represented on a DFD by….

Answer 11

A rectangle, open on the RHS, with the data name (usually noun, never a verb) and a section ruled down the LHS for the ID.

Question 12

A context level DFD represents….

Answer 12

• ONE process only
• terminators (external entities, outside the system)
• system boundaries
• major information flows between entities and the system
NB: Every event should create a response.

Question 13

A level 0 DFD represents at a high level of detail…

Answer 13

• major processes
• data flows
• data stores

Question 14

Differences between a context level and a level 0 DFD include…

Answer 14

A context level DOES NOT show DATA STORES while a level 0 does

Question 15

Stepwise refinement…

Answer 15

Partitions a DFD into the next nested level of intermediate data flow, thereby producing the next level DFD, in order as:
Context level
Level 0
Level 1
Etc…

Question 16

The two main general rules for DFD’s are:

Answer 16

1. The inputs of a process must be different from its outputs
2. All distinct objects in the DFD must have a unique name

Question 17

DFD rules for processes are:

Answer 17

• processes must have both outputs and inputs.

* labels should be verb phrases

Question 18

DFD rules for data stores are:

Answer 18

• all flows to or from a data store must move through a process
• labels should be noun phrases

Question 19

DFD rules for terminators (aka sources or sinks)

Answer 19

• no data moves directly between external entities without going through a process
• labels should be noun phrases

Question 20

DFD rules for data flow are:

Answer 20

• Bidirectional flow between process and data store is represented by two separate arrows.
• Forked data flow must refer to exact same data item (not different data items) from a common location to multiple destinations.
• Joined data flow must refer to exact same data item (not different data items) from multiple sources to a common location.
• Data flow cannot go directly from a process to itself, must go through intervening processes.

Question 21

For a DFD to be balanced means that…

Answer 21

• number of inputs/outputs to lower level DFD equals number of inputs/outputs to associated process of higher- level DFD