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Re: knngist patch support

From: Yeb Havinga <yebhavinga(at)gmail(dot)com>
To: Dimitri Fontaine <dfontaine(at)hi-media(dot)com>
Cc: Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>, Teodor Sigaev <teodor(at)sigaev(dot)ru>, Robert Haas <robertmhaas(at)gmail(dot)com>, Oleg Bartunov <oleg(at)sai(dot)msu(dot)su>, tomas(at)tuxteam(dot)de, "Ragi Y(dot) Burhum" <rburhum(at)gmail(dot)com>, Pgsql Hackers <pgsql-hackers(at)postgresql(dot)org>
Subject: Re: knngist patch support
Date: 2010-02-14 16:01:28
Message-ID: 4B781E58.4060300@gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
Dimitri Fontaine wrote:
> Then there's the metric space which is a data type with a distance
> function. This function must be non-negative, commutative, etc.
>
> So I guess what we need here is a Operator Group to define our plus and
> minus operators, and the fact that it's a group says (by convention,
> like the total ordering of a BTree) that the + is commutative and the -
> its opposite. Or we have an "option" called abelian for specifying the
> commutativity?
>   
Would the group analogy work with partially ordered domains, e.g. with a 
location on a sphere datatype together with an identifier for the sphere 
- so poi on earth can be compared to another, but not a poi on earth 
with a poi on the moon. ?

regards,
Yeb Havinga

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