Concurrency in web services

In earlier days concurrency was something that operating system kernel
designers worried about. To the extent that concurrency was a property
of the hardware it was up to the kernel to control it. The process
model of early operating systems limited concurrent interactions to
the kernel.

Today concurrency has leaked into application programs. Rich GUIs
(Graphical User Interfaces) must respond to user events while other
activities are in progress. Concurrency is inherent to distributed
applications, which must process messages arriving asynchronously from
peers. In particular, high-throughput servers must process concurrent
requests from many clients.

In this context, we look at a variant of web service systems, the
client-server systems with unbounded agents, and propose an automata
based model. We also show that these are equivalent to vector
addistion systems with states (VASS). Therefore, reachability in such
systems is decidable even though the state space is, in general,
infinite. If time permits, we also discuss temporal logics to reason
about such web service based systems.