  ANDy , Activity Networks with Delays, is a discrete time framework aimed at
the qualitative modelling of time-dependent activities. The modular and concise
syntax makes ANDy suitable for an easy and natural modelling of time-dependent
biological systems (i.e., regulatory pathways). Activities involve entities
playing the role of activators, inhibitors or products of biochemical network
operation. Activities may have given duration, i.e., the time required to
obtain results. An entity may represent an object (e.g., an agent, a
biochemical species or a family of thereof) with a local attribute, a state
denoting its level (e.g., concentration, strength). Entities levels may change
as a result of an activity or may decay gradually as time passes by. The
semantics of ANDy is formally given via high-level Petri nets ensuring this way
some modularity. As main results we show that ANDy systems have finite state
representations even for potentially infinite processes and it well adapts to
the modelling of toxic behaviours. As an illustration, we present a
classification of toxicity properties and give some hints on how they can be
verified with existing tools on ANDy systems. A small case study on blood
glucose regulation is provided to exemplify the ANDy framework and the toxicity
properties.
