$${\rm I}.\,\,\,\,\,\,$$ The content diagram should depict the system as a single bubble.
$${\rm II}.\,\,\,\,$$ External entities should be identified clearly at all levels of $$DFDs$$
$${\rm III}.\,\,$$ Control information should not be represented in $$DFD$$
$${\rm IV}.\,\,$$ A data store can be connected either to another data store or to an external
$$\,\,\,\,\,\,\,\,\,\,\,\,$$entity.