Shared Objects - Classes 
The following graphic shows the hierarchy of the global classes that are involved when you work with shared objects.
The CL_ABAP_MEMORY_AREA class is the common superclass of all area classes.
The CL_SHM_AREA class is the superclass of all area classes that are generated when an area is created using transaction SHMA.
The CL_IMODE_AREA class is a predefined area class that enables the current internal session to be handled as an area instance. Its instances are handles for the current internal session.
The <area> classes are generated when an <area> area with the same name is generated in transaction SHMA. Its instances are used as area handles of this area.
Furthermore, there is an IF_SHM_BUILD_INSTANCE interface, which has to be implemented by the class for the optional <area_constructor> area constructor.
