A method for behavior analysis and modeling of entities in conceptual database design based on the entity-relationship approach is discussed. For this purpose, the notion of instantiation of entities is introduced. Behavior of entities, which is defined as a set of transactions and states that result from transactions, is analyzed and modeled using the notion of instantiation and the diagrammatic technique of Petri nets. A formalization of behavior descriptions, together with the notion of transaction normalization, is proposed.