events

hi monu,

PBO - This event is triggered before the screen is displayed.

PAI - This event is responsible for processing of screen after the user enters the data and clicks the pushbutton.

To read data from a database tables we use logical database.

A logical database provides read-only access to a group of related tables to an ABAP/4 program.

adv:-

The programmer need not worry about the primary key for each table.Because Logical database knows how the different tables relate to each other,and can issue the SELECT command with proper where clause to retrieve the data.

i)An easy-to-use standard user interface.

ii)check functions which check that user input is complete,correct,and plausible.

iii)meaningful data selection.

iv)central authorization checks for database accesses.

v)good read access performance while retaining the hierarchical data view determined by the application logic.

disadv:-

i)If you donot specify a logical database in the program attributes,the GET events never occur.

ii)There is no ENDGET command,so the code block associated with an event ends with the next event

statement (such as another GET or an END-OF-SELECTION).

plz reward points if helpful..

Hi,

Process Before Output(PBO):

This event is triggered before the screen is displayed.

The processing of screen before the screen is displayed is done in this event.

For example, filling in default values in the screen fields.

Process After Input (PAI):

This event is responsible for processing of screen after the user enters the data and clicks the pushbutton.

Function code plays an important role in this operation.

Logical databases are special ABAP programs that retrieve data and make it available to application programs. The most common use of logical databases is still to read data from database tables by linking them to executable ABAP programs.

-->they have inbuilt selection-screen

-->you want to improve response times, logical databases permit you to take a number of measures to achieve this (for example, using joins instead of nested SELECT statements). These become immediately effective in all of the application programs concerned and save you from having to modify their source code.

check this link

http://help.sap.com/saphelp_nw04/helpdata/en/9f/db9b5e35c111d1829f0000e829fbfe/content.htm