Chapter 7 Logical Modelling

Question 1

Purpose of Data Flow Diagrams

Answer 1

• to show the processes where data undergo in a system
• to show how data moves and changes through an IS

Question 2

External entities

Answer 2

They are a person, department
(People that interacts with the system)
- may be a source and sink

Question 3

Source and Sink

Answer 3

Source - an external entity that supplies data
Sink - an external entity that receives data

Question 4

Process

Answer 4

Is named to identify the function it accomplishes

Question 5

Data Flow

Answer 5

Representing a specific piece of data such as student ID and names

Question 6

Data Store

Answer 6

is used when the system must store data.
- processes may need to use the stored data at a later time

Question 7

Context Diagram

Answer 7

-DFD (data flow diagram) shows the scope of the system boundaries, external entities that interacts with the system and major information flows between the entities and the system

Question 8

Lower-level diagrams

Answer 8

• Also called child diagram
• Is exploded from parent diagram
  Leveled
• also called exploded, drawn in a detailed diagram until the desired goal is reached
  Balanced
• maintaining consistency among the entire diagrams

Question 9

Diagramming Mistakes in DFD

Answer 9

Inputs but No Outputs - Black Hole
Inputs Not Sufficient To Produce Outputs - Grey Hole
Outputs but No Inputs - A miracle

Question 10

Level 0 DFD

Answer 10

Level 0 -
1. Identify related process - main functionalities
2. Identify data flows to/from external entities to/from identified processes and identifying the data store that is needed

Question 11

Level 1 DFD

Answer 11

• Must use levelling and balancing techniques
  Levelling Example
• Uses detailed DFD’s to describe an IS
• Exploding and decomposing