[Date Prev][Date Next] [Chronological] [Thread] [Top]

RE: ldap PICS

At 23:20 06.06.98 +0000, David Chadwick wrote:
>This is not quite true. ISO also has SHALL and MAY, SHALL being 
>equivalent to IETF MUST. The ISPs are there to sort out which MAYs 
>should be implemented and which should be ignored. Consider 93 X.500 
>replication - all of it is MAY in the standard. How do you get 
>interworking if none of it is mandatory, and the number of options in 
>the MAYs is large. Answer, the ISP on replication. This is what ISPs 
>are for - to sort out which MAYs to implement, not the SHALLs/MUSTs.

Are you saying that if DISP was a separate standard, all the required MAYs
in its specification would be MUSTs, and there would be no need for
the ISP?
In IETF standards, this is usually a "conditional MUST" - you MAY
support this feature, but if you do, you MUST do this other thing.
Example: You MAY support IPSec, but if you do, you MUST support 3DES.

Hard to do right with monolithic protocols, and can easily be confusing
if done as "base protocol plus extensions", like LDAP is trying to do.
(LDAPEXT folks: Take care!)

>BTW, just what does IETF SHOULD mean - by pure logic if a feature is 
>not MUST then it must be MAY, is it not? (Work that one out :-)

SHOULD is an indication that not doing it is stupid in most cases, but
interworkable. Or that's how it SHOULD be :-)
Yes, by Aristotelean logic it's equivalent to MAY. But Aristotelean logic
is not a complete tool for describing real-world operation.

                   Harald
-- 
Harald Tveit Alvestrand, Maxware, Norway
Harald.Alvestrand@maxware.no