As state-based formalisms and object-oriented development methods meet, statecharts represent a natural choice for object behavioural modelling. This is essentially due to built-in features that enforce modularity and control complexity. The paper suggests the improvement of the effectiveness of the statechart approach in achieving both modularity and reuse of behavioural abstractions by analysing the general problem of modelling parts and wholes. An extended statechart construct is proposed, which improves the capability of separating global from local contexts in the early phases of the object development process, achieving better global software quality factors.