Explain briefly the interfacing of CAD database with other software
packages such as CAD/CAM. eg;From CAD linking in with a CNC machine

When you say "database," do you mean a database-driven PDM (Product
Data Manager) such as IBM's VPM (Virtual Product Manager) or
Dassault's EnoviaVPM or some generic MetaPhase-based PDM system -- or,
do you take "database" to simply mean CAD data?

Are you asking how you can get CAD data from one particular design
software (ie, AutoCAD) into some CNC machine's software (ie,
Brown&Sharpe's PCdmis)?

Since you stipulate a CNC machine as your target, I presume you are
the owner/operator of such a machine.  If you could be more specific
about the manufacturer or your CNC equipment, it would enable a
researcher to better answer your inquiry.  Different CNC
hardware/software have different requirements and compatibilities.

Usually, when you are going from CAD drawings to something to be
milled or fabricated . . . there is an intermediate format called STL.
 The CAM software will make the appropriate calculations on the STL
file and send commands to the machine.