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Re: How indexes work in LDAP

> Can someone help explain how indexes work in LDAP.
> From http://www.openldap.org/doc/admin/slapdconfig.html
> *********
> This directive specifies the indexes to maintain for the given attribute. If
> only an <attrlist> is given, the default indexes are maintained.
> Example:
>         index default pres,eq
>         index objectClass,uid
>         index cn,sn eq,sub,approx
> The first line sets the default set of indices to maintain to present and
> equality. The second line causes the default (pres,eq) set of indices to be
> maintained for objectClass. The third line causes equality, substring, and
> approximate indices to be maintained for cn and sn attribute types.
> *********
> I kind of get it, but what do pres,eq,approx,sub,none mean?  
> What does <attrlist> ::= <attr> | <attr> , <attrlist> amount to in human
> speak?

It's BNF, Backas Naur Format.  It means that <attrlist> is defined as
either an <attr> *or* and <attr>, followed by a comma, followed by
an <attrlist>.  In simple terms, it means that <attrlist> is either
a single <attr> or a list of <attr> separated by commas.

Doesn't everybody speak BNF?  :-)