Prova Developers Blog

This post discusses some arguments in favour of joining together the workflow logic with event processing. Typically, event processors and, in particular, stream processors detect event patterns, i.e., groups of events related by temporal relationships and meeting constraints on their content. Event detection is usually an all-or-nothing affair, so that a composite event is either detected or not, in which case nothing happens.

This post gives more details on the approach to event patterns now being added to the new Prova version. As explained in the previous article, the main idea is to group event reactions and associate an operator to the group. I use a term event channel to refer to each reaction that is a member of a reaction group. The new version introduces a variety of annotations that fine-tune the semantics of a reaction group. We make a distinction between control channels and ordinary signal channels.

Event algebras are a formalism for describing composite events that are groups of other events satisfying specified algebraic constraints. We wish to embed event algebra into the Prova language in the simplest, most natural way, allowing Prova rulebases to detect situations arising from events arriving according to pre-defined temporal patterns.

This post is updated according to a revised approach to event algebra. More details will be given shortly. The previous article http://prova.ws/csp/node/20 described the use of the @timeout annotation for imposing a time constraint on arrival of messages. This allows sequential event patterns to be defined quite easily. A further extension of this idea is to use annotations to group reactions. This post describes one such annotation that we call an OR-group (defined using the @or operator annotation).