slapd modules

["Gene Ma" <gma1@home.com>]

In OpenLDAP 2.0 Administrator's Guide section 1.4, it states:

"slapd consists of two distinct parts: a front end that handles protocol
communication with LDAP clients; and modules which handle specific tasks
such as database operations."

I need some helps on how this statement reflects source files in
~/servers/slapd, in which some sub-directories handles backend databases,
and backend.c handles linkage between front end to the specific database. If
this is the right reading, I assume that all the *.c files except backend.c
under ~/servers/slapd are belong to the front end part. Am I right?