Path: utzoo!attcan!uunet!munnari.oz.au!bruce!trlluna!rhea!exner
From: exner@rhea.trl.oz (Rolf Exner - css)
Newsgroups: comp.protocols.iso
Subject: Re:  X500: Does alias have to point to an existing entry?
Message-ID: <742@trlluna.trl.oz>
Date: 2 Oct 89 04:17:08 GMT
References: <8909142001.AA29457@emu.ncsl.nist.gov>
Sender: root@trlluna.trl.oz
Lines: 30

(My mail access has been down for a while)

From article <8909142001.AA29457@emu.ncsl.nist.gov>, by colella@EMU.NCSL.NIST.GOV (Richard Colella):
> 
> Yes, you can create an alias that points to a non-existent entry.
> The decision to let this happen was made a couple of years ago.
> The standards folks decided that the tradeoff between the complexity
> and cost of guaranteeing aliases appeared to outweigh the necessity
> of having this feature.

Supporting guaranteed aliases is complex and operationally costly
when the alias points to an entry in a remote DSA. (Note that
current extensions work in CCITT/ISO on X.500 is again looking at 
supporting such aliases as a second kind of alias)

Yet this does not mean that aliases that point to non-existent objects
have to be retained by a DSA. Directory management actions, outside
the scope of the standards, may delete such dangling aliases whenever
they are detected - e.g on receipt of an aliasProblem NameError.
X.500 makes no guarantee that an entry created one day (and not removed
via RemoveEntry) will be there the next.

A DSA may also elect to keep its own house on order and prevent the
creation of alias entries that it *knows* point to a non-existent 
entry (X.511, 11.1.2.2 notwithstanding). It can do this simply by
returing an unwillingToPerform ServiceError on the basis that it
violates local administrative policy.

Rolf Exner
Telecom Australia Research Laboratories.