The document explains the concept of reactive systems through transition systems, which consist of a set of states and transitions influenced by external events or actions. It defines essential terms like states, transitions, and terminal/deadlock states, using examples such as traffic lights and program execution. Additionally, it covers basic hardware circuits and outlines how states and transitions can be represented mathematically.

1. Bilal Arshed
FA-2017-BSIT-088
Aqsa Khalid
FA-2017-BSIT-081
Amir Numan
FA-2017-BSIT-102

2. • Reactive System
• The intuition is that a transition system consists of a set of possible states for the system
and a set of transitions - or state changes - which the system can effect.
• When a state change is the result of an external event or of an action made by the system,
then that transition is labeled with that event or action.
• Particular states or transitions in a transition system can be distinguished.

3. • model to describe the behavior of systems
• digraphs where nodes represent states, and edges model transitions
• state:
• the current color of a traffic light
• the current values of all program variables + the program counter
• the value of register and output
• transition: (“state change”)
• a switch from one color to another
• the execution of a program statement
• the change of the registers and output bits for a new input

5. • A transition systems is a tuple 𝒜 =< 𝑆, 𝑆0, 𝑇, 𝛼, 𝛽 >where
• S is a finite or infinite set of states,
• 𝑆0 is initial location
• T is a finite or infinite set of transitions,
• 𝛼 and 𝛽 are two mapping from T to S which take each transition t in T to the two states 𝛼(𝑡) and 𝛽(𝑡),
respectively the source and the target of the transition t.
• A transition t with some source s and target s’is written t : s→s’.
• Several transitions can have the same source and target.
• A transition system is finite if S and T are finite.

14. • A path of length n, n >0, in a transition system𝒜is a sequence of transitions 𝑡1,
𝑡2 ⋯ 𝑡 𝑛,such that
∀𝑖: 1 ≤ 𝑖 < 𝑛, 𝛽 𝑡𝑖 = 𝛼(𝑡𝑖+1), and 𝛼 𝑡1 = 𝑆0
• Similarly, an infinite path is an infinite sequence of transitions 𝑡1, 𝑡2, ⋯ 𝑡 𝑛, ⋯such that
∀𝑖: 1 ≤ 𝑖 < 𝑛, 𝛽 𝑡𝑖 = 𝛼(𝑡𝑖+1), and 𝛼 𝑡1 = 𝑆0

15. • Some basics of hardware Circuit/Gate
• OR
• AND
• NOT
• XOR
What are the function of Circuit ?

23. • How to get state ?
• From the value of:
• X
• Y
• R

27. • Let T be a transition system. A state s is a terminal state of T if there are no state s’ such
that s → 𝑠′
.
• A state s is a deadlock state of T if s is reachable and terminal.

29. • Input variable x, output variable y, and register r
• Output function ¬(𝑥 ⊕ 𝑟) and register evaluation function 𝑥 ∨ 𝑟

30. • The state space of a program can be captured by the valuations of the variables and the
program counters
• For our example, we have
• two program counters: pc1, pc2, domains of the program counters: {out, wait, cs}
• three boolean variables: turn, a, b, boolean domain: {True, False}
• Each state of the program is a valuation of all the variables

31. Summary

32. Questions?