Dialogues are an integral and intuitive communication mode for humans to reach a consensus and for their effective application to human-robot interaction a formal model of their structure is required. Formalization of dialogues enable robots to have constructive interaction and management of dialogue breaches such as ambiguity, sudden topic change and misunderstanding. In line with viewing dialogues as collaborative, a formal model of dialogues is proposed through Cooperative Distributed Grammar Systems (CDGS), which are abstract models based on ‘Blackboard problem’ in Artificial Intelligence, for building multi-agent systems, through formal grammars. For this research formalisation is done in two stages: first, a corpus of movie scripts is selected, and annotated with the help of an annotation scheme (combination of speech acts, response and social obligation tag). Then the annotated labels are structured through dialogue policies (progressive, binding and co-occurring) proposed in this paper. Finally, formalization of derived structure through CDGS is done.