A Logical database is an ABAP Program that reads the data from database tables and makes the data avaliable to the ABAP Programs. The Logical database provides a system generated selection screen. The ABAP program must specifically refer to the logical database name in the program attributes. The Coder does not have to worry about the screen design or coding any SQL in order to get the required data. The logical database handles it automatically.
The logical database is hierarchical in structure composed of several nodes. A developer can control the depth of the data retrieval by using the GET <NODE> statement. It may not be a good idea to use a logical database if the only data your program requires is in the last node of a deep hierarchy. The more performance friendly approach would be to program the data retrieval.
The developer can call the logical database directly from the ABAP program using the function module LDB_PROCESS.