1. Automata-Based Programming
General Purpose Finite State Machines
Daniela Kolarova

2. Agenda Automata-Based Programming Applications
Finite State Machine Definition
Finite State Machine Example
FSM Model Simplification
FSM Design Approaches
What We Achieved …

3. Automata-Based Programming
“A programming technique in which the program or part of it can be thought of as a model of a FSM.”
Introduced on a Multiagent systems conference by N. Polikarpova and A. Shalyto (authors of the book “Автоматное программирование”);
Warren McCulloch and Walter Pitts, two neurophysiologists, were the first to present a description of finite automata (“A Logical Calculus Immanent in Nervous Activity”);
Marvin Minsky – Computation: Finite and Infinite Machines, Prentice-Hall;
2015 Spring StateMachine Framework.

4. Automata-Based Programming Applications
Transformation systems – compilers, archivers;
Interactive systems – text editors;
Reactive systems – telecommunication systems, hardware controllers;

5. Automata-Based Programming Applications
Finite State Machines in Hardware
Programming Language Compilers
Workflow Modeling
Game Programming
State Machines Replication (Implementation of Fault-Tolerant Services)

6. FSM Definition
An abstract machine that can be in exactly one of finite number of states at any given time where:
The FSM can change from one state to another in response to some external inputs;
The change from one state to another is called a transition;
A FSM is defined by a list of its states, its initial state, and the conditions for each transition.

7. FSM Model Simplification
Set of States and a defined Start State Set of Inputs Set of Outputs Transition function: Input(I) x State(S) -> State(S') Output function: Input(I) x State(S) -> Output(O) or State(S) -> Output(O)

8. FSM Example: Subway Turnstile SM
State Transition Diagram State Transition Table
Locked
Unlocked
pass/alarm
pass/lock
coin/unlock
coin/thankyou
State
Event
Action
Locked
pass
alarm
coin
unlock
Unlocked
lock
thankyou

9. FSM Design Approaches Nested Switch/Case Statements
Complex code - hard to understand and change/extend;
No separation of FM logic and actions;
No way to send data to a specific state;
Not thread safe.

10. FSM Design Approaches
State Design Pattern: Allows an object to alter its behavior when its internal state changes.

11. FSM Design Approaches State Design Pattern:
Strong separation between actions and the SM Logic;
Explicit transitions defined in the states;
Distributed logic across states;
Tight coupling between state and context.

12. FSM Design Approaches State Transition Table:
Transition logic defined on one place;
Adding new transition requires insertion of a row in the table;
Efficiency increases if the list is replaced by a Map/HashMap;
Readability increases if the construction is implemented via Builder and fluent API;
The table defined can easily be validated against the graphically defined one.

13. What We Achieved …
Transition logic defined on one place and avoided the traversal of all transitions using a HashMap;
Java 8 Features appliade - lambda expressions are optional;
Unified Unit testing of all approaches;
The Action interface can be used as a wrapper for parallel tasks execution;
The example can be easily transformed into a generic state machine and reused.

14. References
Polikarpova N. I., Shalyto A. A. Automata-Based programming,
Volnei A. Pedroni, Finite State Machines in Hardware Theory and Design (with VHDL and SystemVerilog)
Robert C. Martin (2003) Agile Software Development, Principles, Patterns, and Practices 1st Edition, Prentice Halle
Erich Gamma, Richard Help, Ralph Johnson, John Vlissides. Design Patterns: Elements of Reusable Object-Oriented Software 1st Edition, Addison-Wesley
David Lafreniere, State Machine Design in C++, Dr Dobb's Journal, May 01, 2000,
FRED B. SCHNEIDER, Implementing Fault-Tolerant Services Using the State Machine Approach: A Tutorial,
Source code with JUnit tests is available at