LDAP was defined by the IETF in order to encourage adoption of X.500 directories. The Directory Access Protocol (DAP) was seen as too complex for simple internet clients to use. LDAP defines a relatively simple protocol for updating and searching directories running over TCP/IP.
An LDAP directory entry is a collection of attributes with a name, called a distinguished name (DN). The DN refers to the entry unambiguously. Each of the entry's attributes has a type and one or more values. The types are typically mnemonic strings, like "cn" for common name, or "mail" for e-mail address. The values depend on the type. For example, a mail attribute might contain the value "email@example.com". A jpegPhoto attribute would contain a photograph in binary JPEG/JFIF format.
LDAP directory entries are arranged in a hierarchical structure that reflects political, geographic, and/or organisational boundaries. Entries representing countries appear at the top of the tree. Below them are entries representing states or national organisations. Below them might be entries representing people, organisational units, printers, documents, or just about anything else.
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