An Introduction to LDAP
http://ldapman.org/articles/intro_to_ldap.html
X509 Wiki
http://en.wikipedia.org/wiki/X.509
Tree structural information directory;
Read heavy, update infrequently;
Standard based, unified interface, wide support;
Push / pull replication ready;
Security and authorization;
Distinguished Name (DN for short):
As with DNS host names, an LDAP directory record's Distinguished Name (DN for short) is read from the individual entry, backwards through the tree, up to the top level.
Base DN = root (see reference for style of base DN; recommendation and required by Microsoft AD: dc=foobar, dc=com)
Under Base DN: containers to separate entries, as OU entries