JSI Tip 5684. Introduction to Lightweight Directory Access Protocol (LDAP).

Microsoft Knowledge Base Article 196455 contains the following summary:

To understand Lightweight Directory Access Protocol (LDAP) better, let'sdiscuss X.500 and Directory Access Protocol (DAP).

In X.500, the Directory System Agent (DSA) is the database in whichdirectory information is stored. This database is hierarchical in form,designed to provide fast and efficient search and retrieval.