ABSTRACT
This chapter focuses on the semantics of what is commonly called simultaneous events, in the presence of dynamic topologies. It provides a unified definition of time, based on the set of hyperreals, which is able to describe models and components while accommodating deterministic executions under structural changes. The chapter establishes the basic assumptions. It considers that the failure to establish these basic assumptions is responsible to the undefined behavior exhibited by many simulation formalisms. The chapter also considers the noninstantaneous assumption that describes the time semantics of modeling instances when subjected to a transition. The Discrete Flow System Specification (DFSS) is a modular formalism able to describe hierarchical event-based systems with time-varying structure. Hyperreals provide a physical interpretation for logical clocks commonly used in distributed systems. The DFSS supports a simpler interface since it applies the input function to all the input values before sending the result to the receiving component.
