Constraints are defined in view of a program implementation. Constraints check program state or variables to maintain data consistency. A constraint component determines a constraint's scope and variables upon which a constraint depends. Program flow is altered so constraints are checked whenever a variable upon which a constraint depends is updated. Optionally, program flow is altered dynamically to re-establish constraints whenever a variable upon which a constraint depends is updated. Re-establishing constraints provides efficiency, since a program flow is altered for a minimum cost based on a present evolving minimum set of active constraint-variable relationships.