RE: [F&O] avg()

Michael:
Thank you for your comments.  The semantics of fn:avg(), and in fact all
the aggregate functions, were overhauled at the last meeting.
Specifically, values of type xdt:untypedAtomic are now always converted
to xs:double and if the input sequence contains a NaN the result is NaN.
If the input sequence is the empty sequence, the empty sequence is
returned.  The wording has also been changed and clarified.  So, I would
like to close the issue we created based on your mail.  Please take a
look at the next version of the F&O and let us know if you are satisfied
with it. 

All the best, Ashok

> -----Original Message-----
> From: Michael Brundage [mailto:xquery@attbi.com]
> Sent: Wednesday, May 28, 2003 6:47 PM
> To: Ashok Malhotra; public-qt-comments@w3.org
> Subject: RE: [F&O] avg()
> 
> Well, the first sentence is already wrong when $arg is the empty
sequence:
> 
> sum(()) div count(()) => 0.0E0 div 0 => NaN
> avg(()) => ()
> 
> So I'd have to say I still don't like it :-)
> 
> -----Original Message-----
> From: public-qt-comments-request@w3.org
> [mailto:public-qt-comments-request@w3.org] On Behalf Of Ashok Malhotra
> Sent: Sunday, May 25, 2003 11:32 AM
> To: Michael Brundage; public-qt-comments@w3.org
> Subject: RE: [F&O] avg()
> 
> 
> 
> Michael:
> Thank you for your comments.  The sentence about date/time values was
a
> cut and paste error.  Clearly you cannot take the average (or sum) of
> date/time values since addition is not defined on them.  I have
removed
> this sentence.
> I have also adjusted the wording based on your other comments.  See if
> you like this better.
> 
> 15.3.2 fn:avg
> fn:avg($arg as xdt:anyAtomicType*) as xdt:anyAtomicType?
> 
> Returns a value of the same type as the items in $arg that is the
> average of the values (computed as sum($arg) div count($arg)).
> 
> If $arg is the empty sequence, the empty sequence is returned.
> 
> Duration values must either all be xdt:yearMonthDuration values or
must
> all be xdt:dayTimeDuration values. For numeric values, the numeric
> promotion rules defined in 6.2 Operators on Numeric Values are used to
> promote all values to a single common type. Values of type
> xdt:untypedAtomic are cast to the type of the other items in $arg. If
> all values in $arg are of type xdt:untypedAtomic they are converted to
> xs:double. After these operations, $arg must contain items of a single
> type or one if its subtypes. In addition, the type must support
addition
> and division by an integer.
> 
> If the above conditions are not met, then an error is raised ("Invalid
> argument to fn:avg()").
> 
> If $arg contains xs:float or xs:double values, NaN values are
discarded.
> 
> For detailed semantics, see section 6.2.8 of [XQuery 1.0 and XPath 2.0
> Formal Semantics].
> 
> 
> All the best, Ashok
> 
> > -----Original Message-----
> > From: public-qt-comments-request@w3.org [mailto:public-qt-comments-
> > request@w3.org] On Behalf Of Michael Brundage
> > Sent: Saturday, May 17, 2003 1:12 PM
> > To: public-qt-comments@w3.org
> > Subject: [F&O] avg()
> >
> >
> > The definition of avg() contains some statements that are
> contradictory
> > and others that are unclear (at least to me).  For example,
> >
> > (0)
> > "$srcval must contain items of a single type or one if its
subtypes."
> >
> > Followed by a description of (for example) how to promote
> > xdt:untypedAtomic
> > into double.  Clearly avg(xs:double(1.0), xs:untypedAtomic(2.0)) is
> valid,
> > but the quoted sentence above would rule it out.
> >
> > (1)
> > "In addition, the type must support addition and division by an
> integer.
> > If date/time values do not have a timezone, the implicit timezone
> provided
> > by the evaluation context is added and the adjusted normalized value
> is
> > used in the calculation."
> >
> > I see several problems with these two sentences:
> >   (a) xs:date and xs:time do not support addition (with themselves),
> but
> > the second sentence implies sequences of dates and times are
allowed.
> > Is avg((xs:time('01:01:01'), xs:time('03:03:03'))) allowed?
> > What about avg(xs:time('01:01:01'))?
> >
> >   (b) What about avg(xs:date('1972-05-13'),
> xs:yearMonthDuration('P31Y'))?
> > These two support addition (with each other) and division by an
> integer.
> >
> > (2)
> > Are the typing rules described here applied to the static or runtime
> types
> > of the arguments?
> > For example, is the expression
> > avg((if ($someRuntimeCondition) then xdt:yearMonthDuration('P1Y')
else
> > xdt:dayTimeDuration('PT1H'),
> >      if ($someOtherRuntimeCondition) then
xdt:yearMonthDuration('P3Y')
> > else
> > xdt:dayTimeDuration('PT3H')))
> > always a static type error, or will it succeed when
> > $someRuntimeCondition=$someOtherRuntimeCondition and fail otherwise.
> >
> >
> > These confusions could be avoided if there were separate average
> > functions:
> > one for the numeric types (backwards compatible with XPath 1.0,
> > non-numeric items in the sequence are promoted to a numeric type);
> > another function (or set of functions) for date/time/dateTime/
> > dayTimeDuration/yearMonthDuration values, say
> >   avg-date(xs:date*) as xs:date?
> >   avg-yearMonthDuration(xdt:yearMonthDuration*) as
> xdt:yearMonthDuration?
> > etc.
> >
> >
> > Best wishes,
> >
> > Michael Brundage
> > Writing as
> > Author, "XQuery: The XML Query Language" (Addison-Wesley, to appear
> 2003)
> > Co-author, "Professional XML Databases" (Wrox Press, 2000)
> >
> > not as
> > Technical Lead
> > Common Query Runtime/XML Query Processing
> > WebData XML Team
> > Microsoft
> >
> 
>

Received on Friday, 3 October 2003 08:02:57 UTC