Thanks for responding.
SORRY , I am a beginner so I may haven't described clearly enough.
for example,the "Airline" has an input field called "DEMO_CONN-CARRID".
It comes from DDIC type DEMO_CONN, now the problem is that how I can gain the value 'AZ' into the program.
AS the book said that I should use the same name and type of an element on the screen to interact.
I'd like define a data object like this :
DATA DEMO_CONN-CARRID type demo_conn-carrid.
But it didn't obtain the value from screen.