The paper is an investigation on how behaviour relates to norms, i.e. on how a certain conduct acquires meaning in institutional terms. The simplest example of this phenomenon is given by the 'countas' relation, generally associated to constitutive rules, through which an agent has the legal capacity, via performing a certain action, to create, modify or destroy a certain institutional fact. In the literature, however, the 'count-as' relation is mostly accounted for its classificatory functions. Introducing an extension of the Petri Net notation, we argue that the structure of constitutive rules cannot be completely captured by logic conditionals, nor by causal connectives, but it can approached by the notion of supervenience.