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Enhancing Program Comprehension with

recovered State Models

Stéphane S. SoméTimothy C. Lethbridge

SITE, University of Ottawa

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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

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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

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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

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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); }}

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State Model RecoveryProcess

State Model ImplementationSpecification• Specifies how state model implemented

• State Variable Used• Routines (and source files)• Idiom

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Statement Tree

Abstraction of parse tree with relevant

information only Provide code

layout Useful for dealing

with statements affecting flow of execution

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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; …. } }

capturesstate variables control flow

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State Transition Graph

States defined as<variable,value>

Transitions change from a

state to another events correspond

to control structure conditions

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Multiple routines(1) Generate partial models

(2) combine

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SRecover

Recovers state models given state implementation specifications

How to find a Specification ?

Traditional code exploration

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Conclusion Supporting additional patterns

table based implementation OO state patterns

Dealing with multiple state variables

Integration with code exploration tools