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.

In this paper a new type of high level Petri nets is introduced for modelling procedures in complex object database applications. Places in these so-called nested relation/transition nets (NR/T-nets) represent schemes of unnormalized (nested) relations. The marking of each place is a nested relation of the respective type. Each transition represents a specific type of operation on the relations in the adjacent places. These operations may not only operate on whole tuples of a given relation but also on sub-tuples of existing tuples. Arcs in a net are inscribed with so-called filter tables which allow to formulate conditions on the specified (sub-) tuples. Each NR/T-net defines a class of possible system procedures.>

LIVING IN A LATTICE is presented as a rule-based query language for an object-oriented database model. The model supports complex objects, object identity, and is-a-relationships. The instances are described by object relations, which are functions from a set of objects to value sets and other object sets. The rule language is based on object-terms which provide an access to objects via is-a-relationships. Rules are divided into two classes: object-preserving rules manipulating existing objects and object-generating ones creating objects with properties derived from existing objects. The derived object sets are included in a lattice of object types. Some conditions are given under which the instances of the rule's heads are consistent, i.e., where the properties of the derived objects are functionally determined by the objects.>