Introducing time in reaction systems

Reaction systems are a formal model of interactions between biochemical reactions. The main observation underlying the formulation of this model is that such interactions are based on two basic mechanisms: facilitation and inhibition. This paper continues the investigation of reaction systems, and in particular, it proposes a formal framework for introducing time into reaction systems. Within this framework one can formally define and investigate notions such as reaction times, creation times of compounds, their life spans, etc.