  Our machines, products, utilities, and environments have long been monitored
by embedded software systems. Our professional, commercial, social and personal
lives are also subject to monitoring as they are mediated by software systems.
Data on nearly everything now exists, waiting to be collected and analysed for
all sorts of reasons. Given the rising tide of data we pose the questions: What
is monitoring? Do diverse and disparate monitoring systems have anything in
common? We attempt answer these questions by proposing an abstract conceptual
framework for studying monitoring. We argue that it captures a structure common
to many different monitoring practices, and that from it detailed formal models
can be derived, customised to applications. The framework formalises the idea
that monitoring is a process that observes the behaviour of people and objects
in a context. The entities and their behaviours are represented by abstract
data types and the observable attributes by logics. Since monitoring usually
has a specific purpose, we extend the framework with protocols for detecting
attributes or events that require interventions and, possibly, a change in
behaviour. Our theory is illustrated by a case study from criminal justice,
that of electronic tagging.
