Finding the program name and table name in debugger in user exit

Hi All,

I am working on a user exit and want to access a table user exit not available in user exit.

For that I need to find a program and an internal table name(defined as global) and then access it using field symbol.

Am trying to do something as follows.

FIELD-SYMBOLS: <fs_xvbap> TYPESTANDARD TABLE OF vbapvb.

  ASSIGN'(SAPMV45A)XVBAP[])'TO<fs_xvbap>.    <<<<<<<<<<<<<<<<<--------------

  IF sy-subrc EQ0.

   "Further logic to access data from <fs_xvbap>

  ENDIF.

However I don't  know how writer came to conclusion that SAPMV45A is the form/include/programme to be used.

Basically how he realized that we can access internal table using SAPMV45A and internal table name as well.

Any help in this regards will be helpful.Thanks in advance.