In this paper, we define a number of tools that we think belong to the core of any toolkit for requirements engineers. The tools are conceptual and hence, they need precise definitions that lay down as exactly as possible what their meaning and possible us

ransaction occurs, a transition in the state machine of the object is taken. The following things happen in this transition: * An event that triggers the transaction is received from the environment of the object. * The guard of the transaction is evaluated. , The action associated with the transaction may cause changes in the system (OOA allows an action to have effects anywhere). 9 The action is sent to the environment of the object. The first and last items are part of the communication structure of the system and will be specified formally when we discuss the object communication model. The second and third items concern the meaning of actions (including their guards). The meaning of actions is specified in the OOA process model and we will turn to the formalisation of this part of a transition after we analyse the process model below.the attributes of the temperature ramp, and the ramp sends an event to itself to transition to the controlling state. 9 Controlling. Upon entry in the controlling state, and henceforth every time the timer expires, the ramp compares the actual cooking tank temperature with the desired temperature and turns the heater on or off accordingly. If the temperature is not high enough, the time is set to 10 seconds. If the temperature is high enough, the ramp sends an event to itself to transition to the complete state. 9 Complete. Upon entry in this state, the ramp sends an event to its environment that it is complete, turns off the heater, deletes the timer and deletes itself. Figure 10 contains an ADFD for the actions performed in the Created state. An ADFD is a collection of processes (represented by ovals) and data stores (represented by two parallel lines) connected by data flows. The processes represent operations performed during the action by objects in the system. For each process in an ADFD, a process description must be produced (not shown here). The data stores in an ADFD contain the states of existing objects of a class, called a class data store, or the states of timer objects, or the current time. There may be data stores of several different classes in one ADFD. There may be at most one data store that contains the current time. Data flows represent the flow of information in the action and are represented by arrows. Processes in one ADFD may be performed by different objects in the system. The allocation of a process to an object class is expressed by the process identifier. In Fig. 10, the following identifiers have been 9chosen: TR for Temperature Ramp, CT for Cooking Tank, and B for Batch. If the ADFD of an action in the state model of one class accesses the object data store of another class then this represents a synchronous. communication between objects of these two classes. These synchronous communications can be represented by an object access model (OAM). The OAM is a directed graph in which the nodes represent objects and the arcs processes that perform inter-object access.5. The Process