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. Nick