[db-wg] AS-NULL

On 15/12/14 16:26, Nick Hilliard wrote:
> On 15/12/2014 16:13, Job Snijders wrote:
>> Can you elaborate on the use of AS-NULL? Isn't it common place to use
>> something like "NOT ANY"?
> "NOT ANY" is not the same as AS-NULL - they're not interchangeable.
>
> AS-NULL is a convenience placeholder token for where might be a need to
> have an empty as-set.  My particular itch today involved needing to use an
> AS-SET of some form, but where the contents didn't particularly matter.  It
> was more convenient to use an empty set rather than a set with some members
> in it because that gave an element of semantic consistency.
>
> There are other similar sets in the various irrdbs, e.g. AS-EMPTY occurs in
> RADB.  This suggests that there is at least one other person in the world
> who needs this sort of construct.
>
I don't see any particular problem with the NCC creating and owning such 
an empty set

Nigel