Using the extended model for view-centric reasoning, EVCR, we focus on the many possibilities for concurrent processes to be composed. EVCR is an extension of VCR, both models of true concurrency; VCR is an extension of CSP, which is based on an interleaved semantics for modeling concurrency. VCR, like CSP, utilizes traces of instantaneous events, though VCR permits recording parallel events to preserve the perception of simultaneity by the observer(s). But observed simultaneity is a contentious issue, especially for events that are supposed to be instantaneous. EVCR addresses this issue in two ways. First, events are no longer instantaneous; they occur for some duration of time. Second, parallel events need not be an all-or-nothing proposition; it is possible for events to partially overlap in time. Thus, EVCR provides a more realistic and appropriate level of abstraction for reasoning about concurrent processes. With EVCR, we begin to move from observation to the specification of concurrency, and the compositions of concurrent processes. As one example of specification, we introduce a description of I/O-PAR composition that leads to simplified reasoning about composite I/O-PAR processes.
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