Enhancing Program Comprehension with recovered State Models

Enhancing Program Comprehension with recovered State Models Stéphane S. Somé Timothy C. Lethbridge SITE, University of Ottawa

State Transition Models can help program comprehension • High-level behavior models • Capture design decisions • Mapped to code • Strong connection between resulting code and state model • Highlighted by use of state implementation idioms • Problem: what if the original state model is lost or has-been altered

State implementation idioms • Non-procedural languages • Based on goto • Procedural (non-OO) languages • Based on control structures (if, switch, …) • Table lookup • Object-oriented languages • Dynamic binding

Procedural idioms (1) void strans() { …. State = state1; /* initial state */ while(1) { switch(event) { case eventA: if (State == state1) a_1(); else a_2(); break; case eventB: if (State == state1) { b_1(); State = state2; …. } } State variable definition • change of a state variable

Procedural idioms (2) void eventB() { switch(State) { case state1: b_1(); State = state2; break; case state2: b_2(); State = state1; break; default: /* error */ exit(0); } } void eventA() { switch(State) { case state1: a_1(); break; case state2: a_2(); break; default: /* error */ exit(0); } }

State Model Recovery Process • State Model Implementation • Specification • Specifies how state model implemented • State Variable Used • Routines (and source files) • Idiom

Statement Tree • Abstraction of parse tree • with relevant information only • Provide code layout • Useful for dealing with statements affecting flow of execution

State Variable Definition Graph (SVDG) void strans() { (5) State = state1; while(1) { switch(event) { case eventA: if (State == state1) a_1(); else a_2(); break; case eventB: if (State == state1) { b_1(); (20) State = state2; …. } } captures state variables control flow

State Transition Graph • States defined as <variable,value> • Transitions • change from a state to another • events correspond to control structure conditions

Multiple routines (1) Generate partial models (2) combine

SRecover Recovers state models given state implementation specifications How to find a Specification ? Traditional code exploration

Conclusion • Supporting additional patterns • table based implementation • OO state patterns • Dealing with multiple state variables • Integration with code exploration tools

Enhancing Program Comprehension with recovered State Models