Context-Aware Process Networks

A special kind of Process Network introduced as an extension to the basic model but that is interesting for our purposes is that of Context-aware Process Networks [van Dijk et al., 2002]. This new model emerges from the addition of asynchronous coordination to basic Kahn Process Networks so process can immediately respond to changes in their context. This situation is very common in embedded systems.

In Context-aware Process Networks, stream oriented communication of data is done through regular FIFO channels but context information is sent through unidirectional register links (REG). These links have destructive and replicative behavior: writing to a full register overwrites the previous value and reading from a register returns the last value regardless if it has been read before or not. Thus, register links are an event-driven asynchronous mechanism. As a consequence, the behavior of a CAPN depends on the applied schedule or context.

A simple example of a system that can be effectively modeled by a context- aware network is a transmitter/receiver scheme in which the receiver needs to send information about its consumption rate to the transmitter so transmission speed can be optimized. The basic transmitter/receiver scheme can be implemented with a Kahn Process Network but in order to implement feedback coordination we need to use the register link provided by context-aware process networks.

Context-aware systems are indeterminate by nature. Unless the indeterminate behavior can be isolated, a composition of indeterminate components becomes a non-deterministic system, which is possible but not practical. Nevertheless as mentioned in [van Dijk et al., 2002] some techniques can be used in order to oraclise indetermination.