What is the Architecture of MDM4A?
MDM4A is made up of three major parts:
- Generic API
- Provider Framework
- C-Kernel
The Generic API is a release independent interface into the SAP NetWeaver MDM API. It is the only layer that application developers should ever directly interact with. It is comprised of publically available Function Modules and Classes.
The Provider Framework is the release specific implementation of the SAP NetWeaver MDM API. As new releases or support packages of MDM are released, new matching version fo the provider framework will be created. 
However the features of the provider framework are always abastracted by the Generic API, causing the least amount of changes to the consuming applications as possible. This protects the application developer from changes within MDM breaking their applications. The Provider Framework is not intended for direct access by SAP's Customers or Partners. The MDM 5.5 SP4 class for the provider framework is CL_MDM_PROVIDER_SP4_PL00.
The Generic API and the Provider Framework are both delivered as part of a SAINT Package (SAP Add-on installed into the system via transaction SAINT). 
Finally there are new Kernel Libraries written in C that are an integrated part of the ABAP stack that provide the low level communication interface to MDM. The C-Kernel is an integrated part of the AS-ABAP Kernel. The file dw_mdm.dll is part of the core disp+work package of the Kernel and is installed into /usr/sap/<SID>/DVEBMGS<Instance Number>/exe just like the rest of the Kernel
