In this report, we propose a formal approach for the design of object-oriented component- based systems using behavioral contracts. This formalism merges interface automata describing communication protocols of components with the semantics of their operations. On grounds of consistency with the object-oriented paradigms, we revisit the notions of incremental design and independent implementability of interface automata by novel definitions of components compatibility, composition, and refinement. Our work is illustrated by a design case study of CBTC railway systems.