About the backend in slapd.conf

[Wang Penghui <wangpenghui@realss.com>]

Hi,all.

I am a really newbie of OpenLDAP.
When i reading the OpenLDAP Administrator Guide 2.1.x, There is a 
paramter named


       backend <type>

I could not get its means from the Guide.
If i use bdb as the database, need i set "backend bdb"?
What's the functions of this parameter?

Sorry for this simple question.
Thank you in advance!

Wang Penghui