In-depth process modelling may have to model to level three
as a minimum, for this is typically where individual steps, procedures,
decision points, objects and resources are identified (for
example, interaction with discreet applications within a Library
Management System such as the catalogue or customer records
databases). Of course, the requirement to drill down three, or
possibly further levels is not an absolute rule as it will be dependent
upon the scale and complexity of the domain, what is being
modelled, and for what purpose.