Use an attribute not present in the specified classobject - ldap

Question

I'm starting out studying LDAP protocol and this is an example of a possible entry that I found while reading:
dn: o=TUDelft, c=NL
o: TUDelft
objectclass: organization
Now I looked for the organization classobject in the core.schema and I found that the only one mandatory attribute is o and in the attribute definition there isn't the c attribute:
objectclass ( 2.5.6.4 NAME 'organization'
DESC 'RFC2256: an organization'
SUP top STRUCTURAL
MUST o
MAY ( userPassword $ searchGuide $ seeAlso $ businessCategory $
x121Address $ registeredAddress $ destinationIndicator $
preferredDeliveryMethod $ telexNumber $ teletexTerminalIdentifier $
telephoneNumber $ internationaliSDNNumber $
facsimileTelephoneNumber $ street $ postOfficeBox $ postalCode $
postalAddress $ physicalDeliveryOfficeName $ st $ l $ description ) )
So my question is: if an entry is defined as beloging to a sort of objectclass (in this case organization) can it use other attribute too?

Answer 1

An LDAP entry can have any attributes that are defined for any of its objectclasses. In your example, the entry has only the one objectclass organization. Thus, that entry must have an o attribute (which it does) and may have any of the other attributes listed in the MUST section of organization's schema definition. If you want the entry to have attributes not in organization's definition, you must add another objectclass that does contain that attribute.
For example, if you add the objectclass organizationalPerson you can then add organizationalPerson's attributes which include street and postalAddress. (Let's ignore the fact that it does not make much sense that an entry be both an organization and a person.)
You said "the attribute definition there isn't the c attribute". The c=NL in the dn o=TUDelft, c=NL is not an attribute, but rather, part of the entry's distinguished name.