The primary purpose of this slapd(8) backend is to PRESENT
information stored in some RDBMS as an LDAP subtree without any
programming (some SQL and maybe stored procedures can't be
considered programming, anyway ;).
That is, for example, when you (some ISP) have account
information you use in an RDBMS, and want to use modern solutions
that expect such information in LDAP (to authenticate users, make
email lookups etc.). Or you want to synchronize or distribute
information between different sites/applications that use RDBMSes
and/or LDAP. Or whatever else...
It is NOT designed as a general-purpose backend that uses RDBMS
instead of LMDB (as the standard MDB backend does), though it can
be used as such with several limitations. You can take a look at
http://www.openldap.org/faq/index.cgi?file=378 (OpenLDAP
FAQ-O-Matic/General LDAP FAQ/Directories vs. conventional
databases) to find out more on this point.
The idea (detailed below) is to use some meta-information to
translate LDAP queries to SQL queries, leaving relational schema
untouched, so that old applications can continue using it without
any modifications. This allows SQL and LDAP applications to
inter-operate without replication, and exchange data as needed.
The SQL backend is designed to be tunable to virtually any
relational schema without having to change source (through that
meta-information mentioned). Also, it uses ODBC to connect to
RDBMSes, and is highly configurable for SQL dialects RDBMSes may
use, so it may be used for integration and distribution of data
on different RDBMSes, OSes, hosts etc., in other words, in highly
heterogeneous environment.
This backend is experimental.
