Michael Ströder writes:
There has been some opinions to use the date form without dashes to be able to restrict the attribute values to numbers by using LDAP syntax 'Numeric String'. But IMHO that's less user-friendly/readable.
You can make it a little friendlier: 'yyyy mm dd'. That makes for Yet Another Date Format which people (and clients) may have to deal with though.
Another variant if you want textual display is to use a string syntax and a format there already are parsers for, like "3 Apr 2008". Then it's the updating client's job to write a correct date. Again, it depends on what kind of clients will read/write the attribute.