[xquery-talk] Re: The State of Native XML databases

Andrew Welch andrew.j.welch at gmail.com
Tue Aug 21 13:16:10 PDT 2007

On 8/21/07, John Snelson <john.snelson at oracle.com> wrote:
> Andrew Welch wrote:
> > On 8/21/07, John Snelson <john.snelson at oracle.com> wrote:
> >> Andrew Welch wrote:
> >>> Isn't the difference that one _looks like_ a date, but the other _is_
> >>> an xs:date.
> >> What _is_ an xs:date?
> >
> > Something you can perform operations on using functions that expect an xs:date.
> That's one possible answer. Of course, the framework allowing you to
> perform operations on the xs:date could easily be storing it as a
> string. Or maybe 3 non-negative integers. Or maybe the number of seconds
> since the year 0. Or...

But it can only do any of those things if you tell it that the String
'2007-08-21' is a date, and not just a String?

Giving <date>2007-08-21</date> to the database can't be enough...

> Another answer is that an xs:date is any string which matches the
> lexical construct defined in the XML Schema spec.

Yes, but again the value in <date>2007-08-21</date> is castable as an
xs:date but you can't perform date operations on it without first
creating an xs:date out of it.

The way I was reading this thread was that if the type information was
stored in the database, the cost of creating the xs:date would be
incurred once and not once per query that uses the value?

Please feel free to point out my misunderstandings, this is all good info.


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