When constructing an information system, it is important to be able to ascertain the information that the system is constructed to bear, which requires exactitude. And yet the literature of information systems development (ISD) does not seem to have provided a mechanism with such exactitude. This paper suggests integrating the framework of Mingers, the situation theory of Barwise, the information flow theory of Devlin and predicate calculus to develop a technique for formulating information flows within human purposeful activities. The idea is to capture information flows within a human purposeful activity from the point of view of the "actor' by means of a set of formal constructs. The result shows that the use of the formal means sheds light on and injects mathematical rigour into the revelation of the information aspect of the activities, which helps the formulation of information requirements for ISD.