On Fri, Feb 16, 2007 at 05:39:24PM -0300, Alvaro Herrera wrote:
> FWIW there's already a type called tinterval that stores (start,end).  I
> don't think it's very much documented; maybe it can be extended or used
> as base for a new, more complete and robust type, indexable in a more
> natural way, etc etc.

The book I cited has a very complete description of the period data type
including details on what extensions to SQL are needed. I am very
interested in starting a robust implementation of the period datatype.

I think the datetime infrastructure will already do most of the needed
parsing and packing of the hard parts of the period datatype (namely the
date and time formats). I will investigate the tinterval to see if it
meets the needs of the PERIOD datatypes.

I agree with focusing on the PERIOD datatype. I think that is a major
part of the foundation for temporal extensions and would have to be
implemented first. Therefore, I present the following plan for getting

1) Focus first on PERIOD(DATE) to keep things as simple as possible.
2) Implement a first cut on the period datatype that only handles
   storing two dates. (Maybe tinterval will get us here for free?)
3) Add information to the datatype for open or closed interval for
   beginning and ending sides of the period.

I could probably have this done in time for the freeze with some
mentoring. I could probably even start implementation of some indices
and operator function for the type. This functionality is what I expect
to have a shot of making an appearance in 8.3. It will be minimally
functional at this point.

The next project will be altering the parser to be able to construct and
operate on PERIOD types with the syntax extensions to SQL in Dr.
Snodgrass's book.

Once all of the syntax is implemented for PERIOD(DATE), the next project
will be to extend to support PERIOD(DATETIME WITH TIMEZONE). Again, I
think the datatime infrastructure will be very useful here.


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