Nigel Titley wrote:
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
Same here, in principle, but... After having a look at some RFCs I'd suggest to rather go for an AS-EMPTY, as the use of AS0 (AS zero or null) seems to have some semantics attached. I may easily be wrong. :-) Wilfried
Nigel