We have noticed two problems with viewing a process as a sequence of events. The first problem is the complete loss of information about potential intra-process concurrency for both sequential and distributed computations, and partial loss of information about potential inter-process concurrency for distributed computations. The second problem is that the resulting reasoning framework does not lend itself to refinement (from sequential computing or a given set of distributed processes) to a preferable set of distributed processes. We argue that it is more natural to view a computation, either distributed or sequential, as a partially ordered set of events. Doing so leads to a view, called passive-space and time view, which we propose. To aid users of the relation "Affects" in developing algorithms, we define vector clocks, that are global logical clocks, so that the relation "Affects", and hence all potential concurrency, between events can be identified from their timestamps assigned.>

The authors define a relation, 'affects', between every pair of events based on a relation 'locally affects' for each process between each pair of events on the process. A mechanism for timestamping events is defined such that 'affects' relation, and so potential concurrency, between events can be inferred from their timestamps. A timestamping mechanism is presented such that potential concurrency can be inferred partially/completely and the extent of such inferring depends on the costs associated with the mechanism. Inferring 'affects' relationship can be used for debugging and for inferring potential concurrency between events in traces of executions.>

The authors define basic units of computation in distributed systems, whether communicating synchronously or asynchronously, as comprising indivisible logical units of computation that take the system from one ground state to another. It is explained how a computation can be viewed as a partial order over the basic units of the computation. The problem of detecting the basic units is considered. One algorithm for creating ground states during a computation in an asynchronously communicating system with FIFO channels is given, and an existing algorithm that implicitly creates ground states in a synchronously communicating system is referenced. The significance of the basic unit is explained, and its applications are given.>