dn construction question

[Jason Schuchert <JSchuchert@lexica.net>]

I'm relatively new to ldap, not having used it in a true deployment
anywhere.  I am a java/xml developer and comfortable with xpath/DOM etc...

I've been thinking about what a hierachically organized xml/dsml document
would look like and have come across a fundamental ldap usage and data
modelling question.  I've been working with ibm's secureway server with
schema validation turned on and have a question.

When constructing an entry, the objectclasses of the entry dictate which
attributes are required.  For the person objectclass, the cn and sn
attributes are required. 

Given a hierarchy like:

dc=example,dc=com
   ou=People
      cn=Joe Cool
	cn=Bobby Bear

where the cn=Joe Cool,ou=People,dc=example,dc=com entry has two attributes:
cn=Joe Cool
sn=Cool

Why can the rdn of this entry include cn=Joe Cool but doesn't have to
include the other required attribute?  Taken another way, is there any rule
about which attributes (required or optional) from an entry must appear as
part of it's dn?

Apologies for such a novice question but I was laying out this psuedo-dsml
document as an example and came up with this question:

<entries>
   <entry rdn="dc=example, dc=com">
      <objectclass>
         <oc-value>top</oc-value>
         <oc-value>organization</oc-value>
         <oc-value>dcObject</oc-value>
      </objectclass>
      <attributes>
         <attr name="dc">
            <value>example</value>
         </attr>
         <attr name="o">
            <value>Commerce Codeworks</value>
         </attr>
      </attributes>
      <entries>
         <entry rdn="ou=People">
            <objectclass>
               <oc-value>top</oc-value>
               <oc-value>organizationalUnit</oc-value>
            </objectclass>
            <attributes>
               <attr name="ou">
                  <value>People</value>
               </attr>
            </attributes>
            <entries>
               <entry rdn="cn=Joe Cool">
                  <attributes>
                     <attr name="cn">
                        <value>Joe Cool</value>
                     </attr>
                     <attr name="sn">
                        <value>Cool</value>
                     </attr>
                  </attributes>
                  <entries/>
               </entry>
               <entry rdn="cn=Bobby Bear">
                  <attributes>
                     <attr name="cn">
                        <value>Bobby Bear</value>
                     </attr>
                     <attr name="sn">
                        <value>Bear</value>
                     </attr>
                  </attributes>
                  <entries/>
               </entry>
            </entries>
         </entry>
      </entries>
   </entry>
</entries>