Re: extended operator classes vs. type interfaces

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.

regards,
Yeb Havinga