Please exmplain n-tier

Feb 23 2014 6:40 PM

I have inherited an n-tier application and I would like some explanation of its way of grouping files.

I guess BAL is the BUSINESS ACCESS LAYER
DAL is the DATA ACCESS LAYER

Any guesses for EAL? Anyone have any idea what EAL is?

Also, why would the file name content in the BAL be the same as the DAL?

http://i67.photobucket.com/albums/h292/Athono/01_zpsdeba4804.png