When to use LDAP over a database?

So why use LDAP? Here is our list of key characteristics which make the (currently) high level of pain worthwhile.

LDAP provides a remote and local data access method that is standardized. It is thus possible to replace the LDAP implementation completely without affecting the external interface to the data. RDBMS systems mostly implement local access standards, such as SQL, but remote interfaces are always proprietary.

Because LDAP uses standardized data access methods, LDAP Clients and Servers may be sourced (or developed) independently. By extension of this point LDAP may be used to abstract the view of data contained in transaction oriented databases, say for the purpose of running user queries, while allowing the user to transparently (to the LDAP queries) change the transactional database supplier.

LDAP provides a method whereby data may be moved (delegated) to multiple locations without affecting any external access to that data. By using referral methods LDAP data can be moved to alternate LDAP servers by changing operational parameters only. Thus, it is possible to construct distributed systems, perhaps with data coming from separate autonomous organizations, while providing a single, consistent, view of the data to its users.

LDAP systems can be operationally configured to replicate data to one or more LDAP servers or applications without adding either code or changing the external access to that data.