Re: Date with time zone - Mailing list pgsql-general

Going back to the date with datetime, follow me with this reasoning:
If you consider a specific date (in a specific time zone) defined as a specific starting point in time (absolute and universal), and a specific ending point in time, one could say that a date is a period of time ranging from 00:00 hs to 23:59:59.9999 (just as some other member list suggested, with which I totally agree), both times tied to a specific time zone.

One could then say that, "Dec 19th (London Time)" goes from "Dec 19th 00:00:00 (London Time)" to "Dec 19th 23:59:59.99999... (London Time)". So, making a reference to Dec 19th (London Time) would make sense as it refers to a specific absolute time frame, or range. This range, could be (or not, but that is not the point) useful for some practical situations, but the impossibility to be able to state a reference to a date, without recurring to some tweaks or patches is sthing that at the least, bugs me a little.

For instance, if you have a server and you want to tell someone it will be up tomorrow, all day long, with that single reference, your buddy knows exactly that it will be up from 00:00:00 of that day (Your Local Time), to 23:59:59.9999 that day (also in your local time), at least in theory, according to what u said.

And "tomorrow" in that sentence, works as an implicit reference to a day, with a time zone, which combined, references a specific absolute time range.

Maybe another thing that goes against this, is that there would seem to be no reasonable applications for that data type, but I recall having the need for this once, and I think that was the first time I would have liked to be able to specify a date along with a time zone. But again, apart from the possible applications, I still think it is a logic data type to have. To be able to reference a specific date, in a specific country, or time zone.

Another example that comes into my mind is that you may have some coupons, that u can only use on "Dec 19th" (London Time).
Then you have others that u can only use on "Dec 20th" (London Time).

You could very well design the db model with a
from "timestamp with time zone"
to "timestamp with time zone"

and you would be done, or you could simply define a single field
day "date with time zome", to be able to reference the same range in a single field.

If you agree with me on the reasoning behind all the latter cases, we can start analyzing the DST complications, which at the moment just seemed to add some complexity that would eventually undermine my attempts to keep my point the simplest I could, to be sure everyone agreed at least on that.

However, I must say, that I find a pattern on what I've just said.
Why limit the tracking of timezones to a specific day, why not to specif months, in the end they are also time ranges.

January (London Time) actually goes from "Jan 1st 00:00:00 (London Time)" to "Jan 31st 23:59:59.99999 (London Time)".
But is different from January (Brasilia Time) which goes from "Jan 1st 00:00:00" to "Jan 31st 23:59:59.999999" (Brasilia Time).

So with this reasoning, I guess months should also be able to go along a timezone reference, and that just starts to sound a little ridiculous. Don't ask me why.

As a conclusion to all this, sorry guys if I am boring you ! I would almost conclude that:

We have two kind of time ranges:

First of them, ABSTRACT time ranges:
This category includes the abstract definitions of time ranges, for example:
1. A day ranges from 00:00:00 to 23:59:59.99999, independently of whichever day you are on. Its just a definition.
2. A month, lets say, January, ranges from "January 1st 00:00:00" to "January 31st 23:59:59.99999", on any given time zone. Its just a definition.
3. A year is also a range that goes from "January 1st 00:00:00" to "Dec 31st 23.59:59.9999", on any given time zone. Its just a definition.

But when you are talking about a specific time range in a specific location, it stops from being an abstract definition, and becomes an INSTANCE of that time range, and as such, it starts to keep track of its time zone: For example.

1. "Jan 1st" for someone living in London, is a time range going from "Jan 1st 00:00:00 (London Time)" to "Jan 1st 23:59:59.9999 (London Time)"
2. "January" for someone living in London, is a time range going from "Jan 1st 00:00:00 (London Time)" to "Jan 31st 23:59:59.9999 (London Time)".
3. The year 2009 for some living in London, is a time range going from "Jan 1st 00:00:00 (London Time)" to "Dec 31st 23:59:59.9999 (London Time)".

So, when speaking of time ranges, i see there are 2 kind of them, ABSTRACT, and INSTANCES, where abstracts are just the definitions, and instances the concrete implementations of an abstract, put in a specific time zone.

What I see then, is a lack of support for localized time range data types, that would be:
1. date with time zone (not supported).
2. month with time zone (but this datatype doesnt even exist in its abstract form)
3. year with time zone (but this datatype doesnt even exist in its abstract form).
4. etc.

So, maybe there is some coherence it not "localizing" a date, because no other time range is being also "localized".
Maybe the discussion should turn into:

Should time ranges be localized? or even normalized?
Some normalization for ranges already exist, since there is already a "date" datatype. Which is nothing more than an abstract definition of a range that goes from 00:00:00 of that specific date, to 23:59:59.9999.

If such normalization exists, should they also be available in a localized form?
Basically, back to the subject of this thread "Date with time zone?"

Just some thoughts.
Comments welcome.

Eduardo.