  Surveillance is a social phenomenon that is general and commonplace, employed
by governments, companies and communities. Its ubiquity is due to technologies
for gathering and processing data; its strong and obvious effects raise
difficult social questions. We give a general definition of surveillance that
captures the notion in diverse situations and we illustrate it with some
disparate examples.A most important, if neglected,component idea is that of the
identity of the people or objects observed. We propose a general definition of
identifiers as data designed to specify the identity of an entity in some
context or for some purpose. We examine the ways identifiers depend upon other
identifiers and show the provenance of identifiers requires reductions between
identifiers and a special idea of personal identifier. The theory is formalised
mathematically. Finally, we reflect on the role of formal methods to give
insights in sociological contexts.
