  Within a global physical theory, a notion of locality allows us to find and
justify information-processing primitives, like non-signalling between distant
agents. Here we propose exploring the opposite direction: to take agents as the
basic building blocks through which we test a physical theory, and recover
operational notions of locality from signalling conditions. First we introduce
an operational model for the effective state spaces of individual agents, as
well as the range of their actions. We then formulate natural secrecy
conditions between agents and identify the aspects of locality relevant for
signalling. We discuss the possibility of taking commutation of transformations
as a primitive of physical theories, as well as applications to quantum theory
and generalized probability frameworks. This "it from bit" approach establishes
an operational connection between local action and local observations, and
gives a global interpretation to concepts like discarding a subsystem or
composing local functions.
