RE: comments on draft-ietf-sming-reqs-02.txt: Discriminated Unions vs. Real Unions

["Durham, David" <david.durham@intel.com>]

> -----Original Message-----
> From: Juergen Schoenwaelder [mailto:schoenw@ibr.cs.tu-bs.de]
> Sent: Friday, June 29, 2001 12:08 PM
>
<snip>
>
> 51: At first glance, it is somewhat confusing that discriminated
>     unions are required while unions are just nice to have. A
>     discriminated union is a more precise form of a union and hence
>     support for unions will fall out when doing discriminated unions.
>     And since discriminated unions are required, the nice to have
>     feature of unions will fall out anyway. There is certainly the
>     issue whether unions without a discriminator are desirable,
>     although arbitrary unions are classified as nice to have here.
> 
>     We are confused (and hungry?)

[Dave] Do you interpret a discriminated union as being able to change the
underlying base type of an attribute? It was suggested that a "real" union
(in C for example) can change the type as well as the semantic
interpretation of an attribute (perhaps even a group of attributes). It was
mentioned that supporting a real union will require that the SMIng adds ANY
to the supported base types (which is not currently supported by SMIv2 or
SPPI). I believe that is why there are two different proposed requirements.
One for discriminated unions (based on a semantic selector for a statically
typed attribute or group of attributes) vs. real union which may also
include a base-type selector.