Database vs LDAP

In a word, LDAP is a special Database.

• Database users define different schemas (tables) for different applications, while LDAP has predefined standard schemas (object class). This makes sure all LDAP implementations can operate the same way. e.g. WordPress and Blogger may use different table names to store user id and user password, but every LDAP server supports the same objectClass "person". Although LDAP gives users the ability to create customized objectClasses or attributes, it's not used much. 

• Every database engine has its own communication protocol even if SQL is standard, while LDAP has a standard protocol so every LDAP client can communicate with any LDAP server. e.g. OpenLDAP client can work well with Microsoft Active Directory, but MySQL client cannot even connect to PostgreSQL.

• LDAP is mainly used for ID management, while Database can be used for any purpose.