Résumé : New generalised definitions are given for the refinement and recursion operators in the calculus of Petri Boxes. It is shown that not only recursion, but also other operators such as sequence, choice and iteration can be viewed as based on refinement. Various structural properties of these operators can be deduced from a general property of (simultaneous) refinement. A partial order based denotational approach for recursion is presented, which yields a unique fixpoint even in unguarded cases. The construction is based on a judicious naming discipline for places and transitions and yields a closed form for the fixpoint.