INFORMATION-SYSTEM BEHAVIOR SPECIFICATION BY HIGH-LEVEL PETRI NETS

The specification of an information system should include a descriptio n of structural system aspects as well as a description of the system behavior. In this article, we show how this can be achieved by high-le vel Petri nets-namely, the so-called NR/T-nets (Nested-Relation/Transi tion Nets). In NR/T-nets, the structural part is modeled by nested rel ations, and the behavioral part is modeled by a novel Petri net formal ism. Each place of a net represents a nested relation scheme, and the marking of each place is given as a nested relation of the respective type. Insert and delete operations in a nested relational database (NF 2-database) are expressed by transitions in a net. These operations ma y operate not only on whole tuples of a given relation, but also on '' subtuples'' of existing tuples. The arcs of a net are inscribed with s o-called Filter Tables, which allow (together with an optional logical expression as transition inscription) conditions to be formulated on the specified (sub-) tuples. The occurrence rule for NR/T-net transiti ons is defined by the operations union, intersection, and ''negative'' in lattices of nested relations. The structure of an NR/T-net, togeth er with the occurrence rule, defines classes of possible information s ystem procedures, i.e., sequences of (possibly concurrent) operations in an information system.