Client Option for Strong References

Here is the promised summary of the conference call discussions related to
this issue.

Issue:  Should the client be able to request creation of a reference whose
referential integrity is not to be enforced?

Scenarios offered in support of this requirement: 

The owner of a target resource needs to take it offline for a short period
of time, say a week.  It would be useful for the references to that target
to stay in place.  During the period when the target does not exist, the
server responds to GET requests with "404 Not Found", but when the target is
restored, the references work again without having to be recreated.

A collection administrator may decide to create references now, in
anticipation of targets being available in the near future.

Arguments:

It is unlikely that a server implementor would allow referential integrity
to be turned on or off.

What are the semantics of dangling references like?  Will they really
reconnect automatically if the target is recreated?  We need to understand
the semantics of dangling references before we can see whether this
requirement makes sense.

It was agreed that if we give the client a choice, it should be at reference
creation time, not at target deletion time.

General discussion about referential integrity:

The best we can expect from any server for referential integrity is best
effort.  Probably referential integrity will be implemented only for cases
where reference and target are on the same server or a family of
collaborating servers.  Even then, it may not be possible (disks may not be
mounted).  Some servers may support multiple back ends, some of which will
preserve referential integrity, while others do not.  The same server may
change over time, supporting referential integrity at some times but not at
others.

Apache will not implement referential integrity for direct references.
Implementing referential integrity must be optional.

Servers may or may not perform consistency operations.  Do clients need to
know whether they do or not?

We decided at Redmond to include referential integrity in the requirements,
but to defer everything related to referential integrity for the protocol.

Judith A. Slein
Xerox Corporation
jslein@crt.xerox.com
(716)422-5169
800 Phillips Road 105/50C
Webster, NY 14580

Received on Wednesday, 7 October 1998 11:47:11 UTC