Coordination through channel composition

Pew is a channel-based exogenous coordination model wherein complex coordinators, called connectors are compositionally built out of simpler ones. The simplest connectors in Pepsilonomega are a set of channels with well-defined behavior supplied by users. Pepsilonomega can be used as a language for coordination of concurrent processes, or as a "glue language" for compositional construction of connectors that orchestrate component instances in a component-based system. The emphasis in Pepsilonomega is on connectors and their composition only, not on the entities that connect to, communicate, and cooperate through these connectors. Each connector in Pepsilonomega imposes a specific coordination pattern on the entities (e.g., components) that perform I/O operations through that connector, without the knowledge of those entities. Channel composition in Pepsilonomega is a very powerful mechanism for construction of connectors. In this paper, we demonstrate the expressive power of connector composition in Pepsilonomega through a number of examples. We show that exogenous coordination patterns that can be expressed as (meta-level) regular expressions over I/O operations can be composed in Pepsilonomega out of a small set of only five primitive channel types.