Journal: ACM Transactions on Information Systems
The specification of an information system should include a description 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-level Petri nets—namely, the so-called NR/T-nets (Nested-Relation/Transition Nets). In NR/T-nets, the structural part is modeled by nested relations, and the behavioral part is modeled by a novel Petri net formalism. 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 (NF2-database) are expressed by transitions in a net. These operations may 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 so-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 transitions is defined by the operations union, intersection, and “negative” in lattices of nested relations. The structure of an NR/T-net, together with the occurrence rule, defines classes of possible information system procedures, i.e., sequences of (possibly concurrent) operations in an information system.
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