Could anybody explain the indexing keywords?

["Gemeiner, Jan" <Jan.Gemeiner@dresdner-bank.com>]

Hey,
I'm using openldap for 2 years, but I never found a place, where someone
describes the indexing keywords. Maybe, that's general database knowledge, I
have no other idea why this chapter is such a short one in the openldap
admin guide.

May anybody help me, what's the meaning of sub (-initial, -any, -final) ,
pres, eq and the other keywords approx und special ? What are "the indices
specified for default"? What is the default, for what? What the hell is
AUTOSUBTYPES.

Is there any source where I can read about that?

Greetings

Jan Gemeiner