VDM (Vienna Development Method) is based on classical set theory in which a set respresents a static collection of objects. The aim of VDM is to be a method and language for specifying a dynamic system. Therefore, many problems remain in it. The most serious deficiency in VDM is the lack of a well-designed structuring mechanism allowing a hierarchical specification of the whole system and the expression of time requirements. This paper proposes the concept of dynamic set with associated operations in order to make a radical solution to the problem. Based on dynamic set theory and VDM notation a dynamic VDM is presented for constructing the specification of a whole software system. Keywords: Dynamic set, Formal specification, VDM, Structured method . Introduction In classical set theory a set represents a static collection of objects, as described in [1][2][3][4]. However, in many circumstances in the real world, changeable collections of objects must be modeled. Take the students of ...