1 Checking Interaction Consistency in MARMOT Component Refinements Yunja Choi School of Electrical Engineering and Computer Science Kyungpook National University

2 Overview MARMOT methodology Component and refinements Interaction consistency A general framework for consistency checking Case example Model checking elevator system Performance improvement through abstraction Discussion

3 MARMOT Methodology Branched from KobrA by Atkinson et. al Designed for the development of embedded systems High quality system through systematic, structured development Components are the focus of entire development process Tree-structured hierarchy of components Flexibility and reuse of components

4 MARMOT Component

5 Refined component Refining component

6 Recursive Development Specification Realization Identification Kpt A Kpt B Kpt D Kpt C Component Reuse COTS Component

7 Example: elevator system

8 Specifying externally visible behavior

9 Quality Control MAMOT supports systematic identification and refinements of a component the principle of “separation of concerns”: specification vs. realization Iterative decomposition and refinements There can be many issues in consistency Structural consistency Behavioral consistency Behavioral consistency between the realization of refined component and the specification of its refining components

10 Interaction Consistency at i th refinement step, the realization of the refined component constrains the environment of the refining components A system is consistent with its environment in its behavior if it either terminates normally or runs infinitely under the infinite sequence of stimuli generated from its environment A system is inconsistent with its environment in its behavior if it terminates abnormally under the infinite sequence of stimuli generated from its environment

11 Process model A component and its environment are specified as two processes P and E, where each of them is represented as a labeled transition system (S p, L p, R p, I p, T p ) and (S e, L e, R e, I e, T e ) A restricted form of process composition of P and E is defined as P↑E = (S p × S e, L p ∪ L e, R p × R e, I p × I e, T p × T e ) where

12 Consistency Model

13 Formal definitions Termination Terminate(P(s))↑E : P terminates to a state s that belongs to the pre-defined set of terminal states T under the environment E P(s) ∧ s ∈ T, If P is a compositional process, P = P 1 ∥ P 2 ∥.. ∥ P n Terminate(P(s)) ↑E if and only if ∀ i, Terminate(P i (s i )) ↑E i, where E i = E ∥ P 1 ∥ P 2 ∥.. P i-1 ∥ P i+1 ∥ … ∥ P n

14 Formal definitions Progressiveness Progress(P(s)) ↑E : eventually, there is a transition out of the state s under the environment E Interaction Consistency Consistent(P(s)) ↑E = Terminate(P(s))↑E ∨ Progress(P(s)) ↑E

15 Model checking consistency Based on the exhaustive search of system state-space Fully automated SPIN: invalid-endstate checking SMV: we can formulate the consistency property in temporal logic and use model checker to verify it Provide counter-examples Need translation to PROMELA or SMV input language A number of translation approaches are available

16 model checking consistency - Framework -

17 Consistency Model in PROMELA

18 Performance issue

19 Abstraction techniques Trigger-based abstraction Abstract the environment so that it contains all the transitions generating a triggering event for the process P, and all the transitions from the initial state leading to the transition Transition reduction collapse several transitions into one if the intermediate transitions do not generate triggering actions for the process P s0s0 s1s1 s2s2 sisi S i+1 t i /a i s0s0 sisi S i+1 t i /a i

20 Performance Improvement

21 Discussion Formal methods can be effective and useful when integrated into development process Our work focuses on the seamless integration There are a number of existing works on UML consistency, refinements, CBD methodology, and the use of model checking However, they mostly focus on one of the issues separately. Hardly any of the earlier works concerns on performance issue when using model checking Environment constraints have been manually identified in the previous works More investigation is needed on optimization and automation Translation and abstraction

22 Thank you!