Logical database in sap

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What is Logical Database ?

Logical database in SAP
The LDB is special type of ABAP program that combines the contents of certain related database tables and retrieve some related data and make itavailable to application programs.

In other words, a LDB is a method by which ABAP programs read and process the data. The sequence in which the data is supplied to the program is determined by atree structure.

The LDB usually consists of the following components:

Structure
Selections
Database programs

Logical databases have a tree structure. A logical database can contain amaximum of 300 tables

SAPDBPNP is the name of the database program for the logical database PNP.

How are logical database used

1.Logical databases when generating an ABAP program

The selectionscreen generated contains the selections (SELECT-OPTIONS AND PARAMETERS) of both the logical database and the program.

The only database-specific selections displayed on the selection screen arethose needed by the program for data retrieval purposes

2. Logical databases at run-time of an ABAP program

At run-time, the system processes the events in the program and in the logicaldatabase in the following order

Before displaying the selection screen, certain initializations (e.g. calculating default values such as key date, etc.) are performed for the selection screen by thelogical database and the program.
The selection screen is displayed and the user enters data in the input fields.

The logical database and the program check that the input is correct and complete, but also that the user has the appropriate authorizations. If an error occurs, some fields are made ready for input again, so that the user can make the necessary correction(s).

In the eventSTART-OF-SELECTION, the ABAP program performs any preliminary work (for ex, importing files).

The logical database reads the selected data and the program processes it within the GET events...
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