and i have added these additional members in the default core.schema :
objectclass ( 1.3.6.1.4.1.1466.101.120.111 NAME 'extensibleObject' DESC 'RFC2252: extensible object' SUP top AUXILIARY )
attributetype ( 2.16.840.1.113730.3.1.34 NAME 'ref' DESC 'named reference - a labeledURI' EQUALITY caseExactMatch SYNTAX 1.3.6.1.4.1.1466.115.121.1.15 USAGE distributedOperation )
objectclass ( 2.16.840.1.113730.3.2.6 NAME 'referral' DESC 'named subordinate reference object' STRUCTURAL MUST ref )