- From: Andy Seaborne <andy.seaborne@epimorphics.com>
- Date: Mon, 28 Feb 2011 14:40:33 +0000
- To: SPARQL Working Group <public-rdf-dawg@w3.org>

(this is just part of the comments message but a part I wanted to check up on) > -------- Original Message -------- > Subject: avg testcase issues (was: Re: syntax error in testcase manifest) ... > From: Jeen Broekstra <jeen.broekstra@gmail.com> ... > 1. testcase aggregates/agg-avg-01 ("AVG") > > This testcase currently assumes a particular precision in xsd:decimal > division, which is not mandated by the XPath definition. XPath defines > that in xsd:decimal operations, rounding is implementation dependent > (see http://www.w3.org/TR/xpath-functions/#op.numeric, near the end of > the section). > > In the test, five numbers of type xsd:decimal are averaged (1.0, 2.0, > 3.5, 2.2, 2.2). The average is computed by executing a op:numeric-divide > on the sum of the five decimals: 11.1/5. The result of this is, as the > testcase defines, 2.22. However, this result increases precision to 2 > decimals (note that the precision of the input is 1 decimal). > > While this is not wrong, it is not the *only* correct answer: an > implementation that would round or truncate to 1 decimal and return 2.2 > as the answer would IMHO also perform the operation correctly. > > To fix this, I would suggest that the testcase numbers are adapted so > that the result of the division when not rounded is of the same > precision as the input. Alternatively, change the test case to work on > floats or doubles, as division behavior is more precisely defined for > those datatypes. The issue seems to be that reading "2.0" is implying a precision of one decimal place in the decimal. This isn't true - XSD decimal must support at least 18 digits of precision and precision is not a facet of the lexical space. http://www.w3.org/TR/xmlschema-2/#decimal """ Note: All ·minimally conforming· processors ·must· support decimal numbers with a minimum of 18 decimal digits (i.e., with a ·totalDigits· of 18) """ 1.0, 2.0 etc are at least 18 digits of precision and the way the decimal is written is not relevant. i.e. In XSD, 2.00 is not promising more precision than 2.0 - they are different ways to write the same value down. """ Precision is not reflected in this value space; the number 2.0 is not distinct from the number 2.00. """ which is a little different from Java BigDecimal where scale is a factor in BigDecimal.equals or some scientific styles where the number of places does imply accuracy. Andy

Received on Monday, 28 February 2011 14:41:11 UTC