[db-wg] AS-NULL
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Nigel Titley
nigel at titley.com
Mon Dec 15 23:42:22 CET 2014
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
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