FROM DATABASE INDX: What is this and how this it work?

Hi,

I have the following statements in one of the programs that I am modifying:

INDX_KEY-FLAG = 'SP'.

INDX_KEY-USERA = SY-UNAME.

IMPORT DATA_TABLE FROM DATABASE INDX(SD) ID INDX_KEY.

What does the last statement mean? How is it able to fill the table DATA_TABLE, and where is the data taken from?

Points will be rewarded and responses will be greatly appreciated.

Thanks,

John