Re: RFC 2596 questions

["David Chadwick" <d.w.chadwick@salford.ac.uk>]

Date forwarded: 	Fri, 20 Oct 2000 09:57:30 -0700 (PDT)
Date sent:      	Fri, 20 Oct 2000 10:56:01 -0600
From:           	"Jim Sermersheim" <JIMSE@novell.com>
To:             	<d.w.chadwick@salford.ac.uk>
Copies to:      	<Mark.Wahl@innosoft.com>, <ietf-ldapext@netscape.com>
Subject:        	Re: RFC 2596 questions
Forwarded by:   	ietf-ldapext@netscape.com

> Getting back to this:
> 
> The example David gives below shows a subtype inheriting from multiple
> supertypes. As of yet, I believe that this is illegal in X.500/LDAP

It might be illegal in LDAP but it is not illegal in X.501.

> and as such might cause problems with existing servers.
> 
> I don't have a good feeling of closure on this subject. We need to
> revise 4.1.5 of RFC 2251 to say one of the following:

>From the 3 options I prefer option 3 from a modelling perspective, 
but pragmatically what are the implementation implications of the 3 
different models (not being a server implementer myself)?

David

> 
> 1) "An AttributeDescription with one or more options is treated as a
> direct subtype of the attribute type without any options" (inserted
> direct)
> 
> or
> 
> 2) "An AttributeDescription with one option is treated as a direct
> subtype of the attribute type without any options. An
> AttributeDescription with more than one option is treated as a direct
> subtype of all the possible AttributeDescriptions that could be made
> up of all lesser combinations the options"
> 
> That description is pretty ugly and could be fixed. It says that
> cn;a;b;c;d is in a direct subtype of: cn;a cn;a;b cn;a;c cn;a;d
> cn;a;b;c cn;a;b;d cn;a;c;d cn;b cn;b;c cn;b;d cn;b;c;d cn;c cn;c;d
> cn;d
> 
> This also tells me that attribute subtype inheritance is at most two
> levels, but infinitely wide (leaf can multiply inherit from any number
> of supertypes)
> 
> or
> 
> "An AttributeDescription with one option is treated as a direct
> subtype of the attribute type without any options. An
> AttributeDescription with more than one option is treated as a direct
> subtype of all the possible AttributeDescriptions that could be made
> up of all combinations the options sans one option"
> 
> Using the former example, this produces:
> cn;a (direct subtype of cn)
> cn;b (direct subtype of cn)
> cn;c (direct subtype of cn)
> cn;d (direct subtype of cn)
> cn;a;b (direct subtype of cn;a and cn;b)
> cn;a;c (direct subtype of cn;a and cn;c)
> cn;a;d (direct subtype of cn;a and cn;d)
> cn;b;c (direct subtype of cn;b and cn;c)
> cn;b;d (direct subtype of cn;b and cn;d)
> cn;c;d (direct subtype of cn;c and cn;d)
> cn;a;b;c (direct subtype of cn;a;b and cn;a;c and cn;b;c)
> cn;a;b;d (direct subtype of cn;a;b and cn;a;d and cn;b;d)
> cn;a;c;d (direct subtype of cn;a;c and cn;a;d and cn;c;d)
> cn;b;c;d (direct subtype of cn;b;c and cn;b;d and cn;c;d)
> cn;a;b;c;d (direct subtype of cn;a;b;c and cn;a;b;d and cn;a;c;d)
> 
> 
> In the context of language tags, the implications might be benign, but
> when combining disparate options some combinations might cause
> problems.
> 
> I personally prefer 1). Though it may be less flexible, It's simpler
> to understand and fits well with the current subtyping model.
> 
> Jim
> 
> 
> >>> "David Chadwick" <d.w.chadwick@salford.ac.uk> 9/23/00 5:11:55 AM
> >>> >>>
> 
> > Yes, I'm reading "direct" into the 2251 statement. David has argued
> > that: cn;lang-en-US;lang-ja is a direct subtype of cn;lang-en-US,
> > which in turn is a direct subtype of cn. Does this also mean that
> > it's also a subtype of cn;lang-ja, 
> 
> Yes, I would say so. The new dual language subtype is a subtype 
> of both single language subtypes. The order does not matter. We 
> have
> 
>                supertype
>              /                  \
> subtype 1                    subtype 2
>               \                 /
>               subtype1-2
> 
> David
> 
> >or is it strictly a right to left thing?
> > If r to l, then the attribute type option ordering restriction will
> > get in people's way.
> > 
> > Jim
> > 
> 
> 
> ***************************************************
> 
> David Chadwick
> IS Institute, University of Salford, Salford M5 4WT
> Tel +44 161 295 5351  Fax +44 161 745 8169
> Mobile +44 790 167 0359
> Email D.W.Chadwick@salford.ac.uk
> Home Page  http://www.salford.ac.uk/its024/chadwick.htm
> Understanding X.500  http://www.salford.ac.uk/its024/X500.htm
> X.500/LDAP Seminars http://www.salford.ac.uk/its024/seminars.htm
> Entrust key validation string MLJ9-DU5T-HV8J
> 
> ***************************************************
> 


***************************************************

David Chadwick
IS Institute, University of Salford, Salford M5 4WT
Tel +44 161 295 5351  Fax +44 161 745 8169
Mobile +44 790 167 0359
Email D.W.Chadwick@salford.ac.uk
Home Page  http://www.salford.ac.uk/its024/chadwick.htm
Understanding X.500  http://www.salford.ac.uk/its024/X500.htm
X.500/LDAP Seminars http://www.salford.ac.uk/its024/seminars.htm
Entrust key validation string MLJ9-DU5T-HV8J

***************************************************