Behaviour of Elementary Net Systems

We consider two ways of recording the behaviour of an elementary net system (EN system): via sequential observations and via non-sequential observations. In the sequential point of view each record of the behaviour of an EN system is a string of event occurrences (called a firing sequence) as registered by a sequential observer. In the nonsequential point of view we can define the behaviour of an EN system by either extracting causal order of events from firing sequences (obtaining firing traces) or by recording all nonsequential observations of event occurrences and of resulting holdings of conditions (each such record is called a process). In our contribution we discuss each of the three approaches and then relate them to each other.