What's a model?

Conceptual Modelling

• A model that is conceptual
  • ​... with a real world correspondence
  • ... without a real world correspondence
• A model of a concept​

Conceptual models software engineers care about

• Data models
• Mathematical models
• Domain models
• Data flow models
• State transition models (today)

How models are used

• To predict future states of affairs.
• Understand the current state of affairs.
• Determine the past state of affairs.
• To convey the fundamental principles and basic functionality of systems (communication)

Communicating models

• Four fundamental objectives of communicating with a conceptual model:
  1. Enhance an individual's understanding of the representative system
  2. Facilitate efficient conveyance of system details between stakeholders
  3. Provide a point of reference for system designers to extract system specifications
  4. Document the system for future reference and provide a means for collaboration

Kung and Solvberg (1986)

State Machines

• Machines made up of a finite number of states.
• The machine can be transitioned from one state to another
• Simple example: a door

State diagrams

• A diagrammatic representation of a state.
• Some variation in notation.
• Typically: states are circles, transitions are labelled arrows connecting them

State machines

• Useful for modelling systems that have clearly defined states. For example:
  • UIs with different screens
  • Network protocols
  • Conversational interfaces

Parking meter

Parking meter

Opal Card

• Can we model the opal card system as a state machine?