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Re: extended operator classes vs. type interfaces

From: Robert Haas <robertmhaas(at)gmail(dot)com>
To: Yeb Havinga <yebhavinga(at)gmail(dot)com>
Cc: pgsql-hackers(at)postgresql(dot)org
Subject: Re: extended operator classes vs. type interfaces
Date: 2010-04-09 14:33:04
Message-ID: s2j603c8f071004090733h1bb2d66ak57de0b479106909a@mail.gmail.com (view raw or flat)
Thread:
Lists: pgsql-hackers
On Fri, Apr 9, 2010 at 7:55 AM, Yeb Havinga <yebhavinga(at)gmail(dot)com> wrote:
> Robert Haas wrote:
>>
>> Under the first type [4pm,5pm) =
>> [4pm,4:59:59pm], while under the second [4pm,5pm) = [4pm,4:59pm].
>>
>> Thoughts?
>>
>
> The examples with units look a lot like the IVL<PQ> datatype from HL7, see
> http://www.hl7.org/v3ballot/html/infrastructure/datatypes_r2/datatypes_r2.htm
>
> About a type interface, the HL7 spec talks about promotion from e.g. a
> timestamp to an interval (hl7 speak for range) of timestamps (a range), and
> demotion for the back direction. Every 'quantity type', which is any type
> with a (possibly partially) lineair ordered domain, can be promoted to an
> interval of that type. In PostgreSQL terms, this could perhaps mean that by
> 'tagging' a datatype as a lineair order, it could automatically have a range
> type defined on it, like done for the array types currently.

The way we've handled array types is, quite frankly, horrible.  It's
bad enough that we now have two catalog entries in pg_type for each
base type; what's even worse is that if we actually wanted to enforce
things like the number of array dimensions we'd need even more - say,
seven per base type, one for the base type itself, one for a
one-dimensional array, one for a two-dimensional array, one for a
three-dimensional array.  And then if we want to support range types
that's another one for every base type, maybe more if there's more
than one kind of range over a base type.  It's just not feasible to
handle derived types in a way that require a new instance of each base
type to be created for each kind of derived type.  It scales as
O(number of base types * number of kinds of derived type), and that
rapidly gets completely out of hand

...Robert

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