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

2 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

3 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

4 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

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

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

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

8 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

9 State Transition Graph States defined as Transitions change from a state to another events correspond to control structure conditions

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

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

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