decoupling of objetct-oriented systems

a strategy of decoupling
1.indenty subsystem
2.Reduce static couping between diffrent subsystem classes
3.Reduce dynamic coupling
Suitable combinations of collaborations reduce coupling but often introduce additional classes
or have other drawbacks. There are several design patterns that describe proven combinations.
Still, they only help if the subsystem division reasonably reflects the problem structure of
your system.
Abstract protocols are the classes that  contain only abstract methods.
 these methods comprise the interface.
a client has to provide user the subsystem.
Hence , the client class has to inherit and implement the abstract protocol.
This is a good way to guarantee complete interfaces.
There are five patterns that deal with different  aspects of decoupling .
all the pattens are from GOF.
managing static realitions
manageing dynamic realitions
encapslating subsystems