As per my experience and knowledge, I don’t think integration exists.SAP includes its own set of mapping strategy called as Open SQL which is flexible to provide some of the special functions like insertion, updation and deletion of the data, allowing to ensure the data consistency, functions being called as BAPI. Also a SAP connector is required to call the BAPI functions
Also it is possible to establish a connection directly to the database. However, this option is not recommended and found to be dangerous as this could lead to inconsistencies in the system. When you are working with the softwares like connectors, you can use the SAP interface system.
There is also one more strategy that is used as an intermediate table on the database where you and SAP are involved in taking and writing the data and establishing communication with each other using some controls. Also you can make use of BAPI if you are using the standard table or the custom table.