System Models

Question 1

System Models

Answer 1

Abstract descriptions of system whose requirements are being analysed. System modelling helps the analyst to understand the functionality of the system.

Question 2

Model Perspectives

Answer 2

External perspective
Behavioural perspective
Structural perspective

Question 3

External Perspective

Answer 3

Shows the system’s content or environment

Question 4

Behavioural Perspective

Answer 4

Shows the behaviour of the system

Question 5

Structural Perspective

Answer 5

Shows the system/data architecture

Question 6

System Model Advantages

Answer 6

• Easier to understand than using natural language description
• Simplifies the attributes (abstraction) compared to a system representation.

Question 7

System Model Disadvantages

Answer 7

• Do not model non-functional system requirements
• Do not include information of whether a method is appropriate for a given problem
• Too much documentation
• System models are often too detailed and difficult to understand for users

Question 8

Model Types

Answer 8

• Data processing model
• Compositional model
• Architectural model
• Classification model
• Stimulus/response model

Question 9

Context Model

Answer 9

Used to show boundaries of the model. Affected by social and organisational concerns.

Question 10

Data Processing Model

Answer 10

Shows how data is processed at different stages

Question 11

Composition Model

Answer 11

Shows how entities are composed of other entities.

Question 12

Architectural Model

Answer 12

Shows principal sub-systems.

Question 13

Classification Model

Answer 13

Shows how entities have common characteristics.

Question 14

Stimulus/Response Model

Answer 14

Shows how system’s react to events.

Question 15

Process Model

Answer 15

Shows overall process and the processes that are supported by the system.

Question 16

Data Flow Model

Answer 16

May be used to show how the processes and the flow of information from one process to another.

Question 17

Behavioural Model

Answer 17

Describes the overall behaviour of the system.

Question 18

Types of Behavioural Models

Answer 18

• Data processing models
• State machine models

Question 19

Data Processing Model example

Answer 19

Data flow Diagram, which shows the processing steps as data flows through a system.
Tracks and documents how data is associated with a process.
Top-down processes.

Question 20

Data Flow Context Diagram

Answer 20

Dotted lines -> control
Solid lines -> data

Question 21

Statechart Diagram

Answer 21

Shows the behaviour of the system in response to internal and external events.

Question 22

Statechart Diagram Context

Answer 22

Initial state -> solid circle
Final state -> two circles
Rounded rectangles -> used for states
Does not show flow of data, and contains a key to understand the diagram better.

Question 23

Labels

Answer 23

Statechart diagram feature.
Denote the methods called to move between two states.

Question 24

Guard

Answer 24

Statechart diagram feature.
Allow movement between states after a certain condition has been fulfilled.

Question 25

Finite State Machines/ Finite State Automata

Answer 25

Models the behaviour of the system or a complex object, with a limited number of defined conditions or modes, where mode transitions change with circumstance.

Question 26

Finite State Machines Context

Answer 26

• set of states
• start state
• input alphabet
• transition function which maps input symbols and current states to a next state

Question 27

State Transitions

Answer 27

Term for moving from one state to another.