1.5. Object Event Modeling and Simulation

Object Event (OE) Modeling and Simulation (M&S) is a new general Discrete Event Simulation (DES) paradigm based on the two most important ontological categories: objects and events. In philosophy, objects have also been called endurants or continuants, while events have also been called perdurants or occurrents.

OEM&S combines Object-Oriented (OO) Modeling with the event scheduling paradigm of Event Graphs (Schruben 1983). The relevant object types and event types are described in an information model, which is the basis for making a process model. A modeling approach that follows the OEM paradigm is called an OEM approach. Such an approach needs to choose, or define, an information modeling language (such as Entity Relationship Diagrams or UML Class Diagrams) and a process modeling language (such as UML Activity Diagrams or BPMN Process Diagrams).

We propose an OEM approach based on UML Class Diagrams for conceptual information modeling and information design modeling, as well as DPMN Process Diagrams for conceptual process modeling and for process design modeling.

In the proposed approach, object types and event types are modeled as special categories of classes in a UML Class Diagram. Random variables are modeled as a special category of class-level operations constrained to comply with a specific probability distribution such that they can be implemented as static methods of a class. Queues are not modeled as objects, but rather as ordered association ends, which can be implemented as collection-valued reference properties. Finally, event rules, which include event routines, are modeled in DPMN process diagrams (and possibly also in pseudo-code), such that they can be implemented in the form of special onEvent methods of event classes.

Like Petri Nets and DEVS, OEM&S has a formal semantics. But while Petri Nets and DEVS are abstract computational formalisms without an ontological foundation, OEM&S is based on the ontological categories of objects, events and causal regularities.

In model-based simulation engineering, we distinguish between (1) a conceptual model describing a real-world problem domain, and (2) a simulation design model defining a certain computational solution for the purpose of a simulation study. Both conceptual models and design models consist of an OE class model describing/defining the system's state structure (in the form of object types and event types, and the associations between them) and a DPMN process model describing/defining the system's dynamics (in the form of causal regularities captured by event rules).

An OEM approach results in a simulation design model that has a well-defined operational semantics in terms of a transition system based on the event rules modeled in a DPMN process design diagram, as shown by Wagner (2017a). Such a model can, in principle, be implemented with any object-oriented (OO) simulation technology. However, a straightforward implementation can only be expected from a technology that implements the OEM&S paradigm, such as the OES JavaScript (OESjs) framework.