Large socio-technical systems impose a number of significant 
challenges, both technical and organisational. Their complexity 
makes all stages of their development (requirements analysis, 
specification, design, implementation, deployment and maintenance/evolution) 
subject to failure and costly re-working. Even the production of 
an unambiguous behavioural description of an existing system is 
far from straightforward. One characteristic of these computer-based 
systems is that they are required to function at many different time 
scales (from microseconds or less to hours or more). Time is clearly 
a crucial notion in the specification (or behavioural description) of 
dependable computer-based systems, but it is usually represented, 
in modeling schemes for example, as a single flat physical phenomenon. 
Such an abstraction fails to support the structural properties of the 
system, forces different temporal notions onto the same flat description, 
and fails to support the separation of concerns that the different time 
scales of the system facilitate. In this talk a framework involving the 
use of time bands will be introduced and elements of a time band model 
will be described.