Object - Oriented Nets with Algebraic Speci cations : The CO - OPN / 2 Formalism ?

Class C-User; Interface Use Coord, Size, Angle, Privilege, Ownership; Type c-user; Methods join _ : privilege; leave; select _ : coord; unselect; go-down; go-back; delete; move _ : coord; resize _ : size; rotate _ : angle; own-for _ : ownership; Body Use Unique, C-Viewport; Places idle _ , active _ : unique; cur-vp _ : c-viewport; Initial idle @; Axioms join pr with v.(self join pr) :: idle @ -> active @,cur-vp v; leave with v.leave :: active @,cur-vp v -> idle @; select p with v.select p :: active @,cur-vp v -> active @,cur-vp v; move p with v.move p :: active @,cur-vp v -> active @,cur-vp v; own-for os with v.own-for os:: active @,cur-vp v -> active @,cur-vp v; where p : coord; v : c-viewport; pr : privilege; os : ownership; ;; ... and more axioms ... End C-User; Spec. 12: The Cooperative Users. and rotate methods are used to modify aspects of selected components. The own-for method represents the user's will to own a component for a given ownership. The instance variables (Places eld) are involved in the behavioral axioms which describe the properties of the methods. For instance, the behavioral axiom join pr with v.(self join pr) :: idle @ -> active @, cur-vp v indicates that the join method is asking to be synchronized with the join method for the privilege pr of an available existing viewport v. The user has to be idle and will become active. Moreover, the free variable v will be uni ed with an available existing viewport and memorized by the current viewport attribute (cur-vp v). The self-reference self informs the viewport of the identity of the user who wants to be connected to it. The viewport will store this object identi er in order to know what connection has been established. The role of the method select is the transmission of the user's will to select an existing component at a given position p to the current viewport v. The same remark holds true for the other methods. Figure 19 provides a partial graphic view of the C-User class. Note that for the sake of clarity not all the methods have been represented. In order to obtain an e ective class of users which may be involved in a hierarchical Petri net editor we make use of inheritance. In Speci cation 13 one may see the inheriting class PN-C-User which inherits from the class C-User as declared under the Inherit eld. In this situation some renamings, declared