Traditional applications architectures have been based on function.
Today, to meet the needs of the business an application architecture
should reflect the complete range of business requirements.

Therefore, client/server computing demands a three layer view of the
organisation.  

1 The user interface layer, which implements the functional model

2 The business function layer, which implements the process model

3 The data layer, which implements the information model

It should be noted that this application architecture does not demand
multiple hardware platforms, although such technology can be utilised,
if the environment is robust and reliable enough and the business is
prepared to pay the additional costs associated with workstation and
LAN technology.