1. Lecture 4 Model checking/OBDDs Design by contract
OCL: Object constraint language for pre and post conditions, invariants etc.
Testing multi-threaded programs
Testing state machines and statecharts

2. Chapter 19: State machines and statecharts
Widely used: graphical user interfaces, networking protocols. Important role in object-oriented design: some objects contain own state machine or state chart. Also useful for multi-object coordination (traversal state).

3. State machine or statechart
Two purposes
model
describes a portion of the system
implementation framework
provides skeleton for implementation

4. State machines May grow large and cumbersome
Therefore, David Harel invented statecharts

5. Statecharts State actions Example on entry on exit
do (called activity)
Example
on entry: notify repair center
on exit: log repair
do: flash service light

6. Statecharts Conditional state transitions
Nested states: very useful. Allow to treat individual state as a state machine. Allow for clear boundaries between parts of the graph

7. Concise artifacts: a comparison
State machine: Statechart
sometimes exponentially smaller
Decision tree: BDD (binary decision diag.)
sometimes exponentially smaller

8. Start (H) Ready Warmup Quality_ Check Copying Alternate_Start Backup_ok
Is_warm
Quality_
Check
stop
start on
Copying
Alternate_Start
Backup_
Check_
Quality
Backup_
Warmup
Is_warm
fault
Error
Low_resolution

9. When and how to build models
If a subsystem has a behavior that could be described with a state model but does not have one, create it. Helps with fault finding.