Abstract
In a previous paper, we developed an algebraic theory about threads and multi-threading based on the assumption that a deterministic interleaving strategy determines how threads are interleaved. The theory includes interleaving operators for a number of plausible deterministic interleaving strategies. The interleaving of different threads constitutes a multi-thread. Several multi-threads may exist concurrently on a single host in a network, several host behaviors may exist concurrently in a single network on the internet, etc. In the current paper, we assume that the above-mentioned kind of interleaving is also present at these other levels. We extend the theory developed so far with features to cover the multi-level case. We use the resulting theory to develop a simplified formal representation schema of systems that consist of several multi-threaded programs on various hosts in different networks. We also investigate the connections of the resulting theory with the algebraic theory of processes known as ACP.