There is a new book on Programming in SAP APO. You might want to check that out.
also please read this :-
LiveCache is a program for high performance management of objects used by APO
application programs (COM Routines). These objects called OMS objects contain
application data whose meaning is unknown to LiveCache. All objects ideally are
located in main memory in the global data cache of the LiveCache -in the global
data cache -of the LiveCache, but may be swapped out to disk in case of memory
COM routines run as stored procedures in the address space of LiveCache and are
called from APO ABAP programs which run on the APO application servers. Due to
the fact that COM routines run in the address space of LiveCache , they have direct
access to OMS objects, and navigation over networks of OMS objects is very fast.
Typical access time is less than 10 microseconds per object.
LiveCache provides classes and class methods to the COM routines to administer
their objects. Technically: COM routines inherit class methods from the LiveCache
base classes to create, read, store and delete OMS objects.
LiveCache relieves the application programs of implementing their own transaction
and lock management. The application program is able either to commit or rollback
all changes made on several objects in a business transaction.
LiveCache ensures the existence of OMS objects beyond the lifetime of COM
routines. That’s why LiveCache uses the term persistent OMS objects. When
LiveCache is stopped or when a checkpoint is requested, all objects are stored on
hard disks. The APO application uses a complex object orientated application
model. This model is easier to implement by an object oriented programming than
with the relational structures of a relational database. Therefore, LiveCache
supports object oriented programming through providing adequate C++
LiveCache provides the application with the concept of consistent views to isolate
the data of an application from simultaneous updates by other users (reader
isolation). COM routines are implemented in LiveCache as stored procedure.
Therefore the call of a COM routine from ABAP is quite simple through using EXEC
ABAP Programs and the APO optimizers use native SQL for communicating
through the standard SAP DB interface to LiveCache. LiveCache has an SQL
interface that is used to communicate with the SAP instances. With native SQL,
ABAP programs call stored procedures in the LiveCache that point to Component
Object Model (COM) routines written in C++. An SQL class provides SQL methods
to access the SQL data through the COM routines.