Foundations of web transactions

A timed extension of pi-calculus with a transaction construct - the calculus Web pi - is studied. The underlying model of Web pi relies on networks of processes; time proceeds asynchronously at the network level, while it is constrained by the local urgency at the process level. Namely process reductions cannot be delayed to favour idle steps. The extensional model - the timed bisimilarity - copes with time and asynchrony in a different way with respect to previous proposals. In particular, the discriminating power of timed bisimilarity is weaker when local urgency is dropped. A labelled characterization of timed bisimilarity is also discussed.