In this work, we propose an approach for regulating agents interaction on an open multi-agent system. In open systems, agents are immersed in a highly unpredictable environment, they can be self-interested, and other agents are frequently unknown beforehand. We argue that, in some applications, unexpected behavior may lead to system faults. For this reason, we propose a law enforcement approach to build open multi-agent systems where a certain degree of control over agents behavior is desirable. A conceptual model is proposed to specify how the interactions of an open multi-agent system should happen. This model deals with concepts such as norms, constraints and scenes in a integrated way. We also propose a declarative language that allows the interaction s specification according to the elements that compose the conceptual model, and a software infrastructure that acts as a mediator monitoring and enforcing agents interaction.