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Jim Melton: XML Query WG review of RIF Datatypes and Built-Ins 1.0

From: Sandro Hawke <sandro@w3.org>
Date: Thu, 24 Sep 2009 21:05:15 -0400
To: public-rif-comments@w3.org
Message-ID: <21958.1253840715@waldron>

Here's the review of RIF from the XML Query WG, forwarded with permission.

attached mail follows:


The XML Query WG has completed its review of RIF Datatypes and 
Built-Ins 1.0 and has developed some comments.  Please note that 
Sharon and I initially agreed to submit the XML Query WG's comments 
and the XSL WG's comments jointly, but my WG objected on the grounds 
that they had not yet seen the XSL WG's comments and did not want to 
wait for them.  Consequently, Sharon will submit the XSL WG's 
comments separately whenever they are ready.


1) Thanks for giving us the opportunity to review this document.  We 
were very pleased to see that you have based much of this spec on the 
Functions and Operators specification that we developed, as well as 
on the XML Schema Part 2 Datatypes spec on which we also 
depend.  There are other W3C WGs whose documents made use of the F&O 
functions, but redefined the functions instead of incorporating them 
by reference.  Your approach is manifestly appropriate.  Thanks!

2) We are slightly concerned by the fact that you state in the 
Overview that "A large part of the definitions of the listed 
functions and operators are adopted from [XPath-Functions]," but that 
you define a different namespace 
for the functions instead of using the defined namespace 
of those functions that have been adopted.  We note that Section 4 
uses the word "adapted" instead of "adopted", which has significantly 
different connotations.  We have concluded from additional text in 
the document that "adapted" is the word that you intended to use and 
recommend that you resolve the discrepancy by correcting the Overview.

3) In section 2.2.1, we read the statement "since xs:duration does 
not have a well-defined value space."  We believe that 
mischaracterizes the rationale for the creation of the types 
xs:dayTimeDuration and xs:yearMonthDuration.  The rationale is 
actually that the xs:duration data type is not fully ordered, while 
the two types derived from xs:duration are fully ordered.  It is 
unlikely that XML Schema will be able to redefine xs:duration in a 
way that is both compatible and fully ordered.

4) Also, in section 2.2.1, since xs:dateTimeStamp is taken from XSD 
1.1, it would also make sense to take xs:dayTimeDuration and 
xs:yearMonthDuration from XSD 1.1, rather than from XDM. The 
definitions are equivalent by design. (This also affects section 2.3.)

5) In section 2.3, the type hierarchy for integer subtypes appears to 
be incorrect.  unsignedLong should not be a subtype of 
positiveInteger (because it allows the value zero). Also the prefix 
"xs:" is included or omitted indiscriminately.

6) In section 4.3, we learn that "Itruth Iexternal( ?arg1; 
pred:is-literal-not-DATATYPE ( ?arg1 ) )(s1) = t if and only if s1 is 
in the value space of one of the datatypes in 
but not in the value space of the datatype with shortname DATATYPE, 
and f otherwise."  We believe that means that the predicate 
pred:is-literal-not-integer returns f if the value of its argument is 
not in the value space of any datatype in DTS!  If that is true, then 
it is highly misleading, because returning false implies that the 
value is a literal of type integer.  We recommend that you reconsider 
this definition so that the predicate returns true when the value is 
either (a)not in the value space of any datatype in DTS or (b)is in 
the value space of some data type in DTS but not in the value space 
of the specified datatype.

7) In section 4.4.1, we discovered the trivial typographical error 
"funcitons".  We also noticed the trivial typographical error "ab" 
(should be "an").

8) In section 4.5.1, Numeric functions, it is not clear whether 
functions such as func:numeric-add accept arguments of mixed type 
(e.g. integer plus double).  Although neither sections 1.3, 1.4 and 
6.2 of Functions and Operators nor appendix B of XPath 2.0 are 
wonderfully clear on the point, our reading is that the underlying 
function op:numeric-add() does not accept mixed arguments; rather, 
when the XPath "+" operator is applied to an integer and a double, 
the integer is promoted to a double and the function 
op:numeric-add(double, double) is called. The operator accepts 
mixed-type arguments, but the underlying function does not. (Others 
may disagree with this reading, as it really isn't 100% clear.)

9) Section Note that for reasons that are entirely 
paternalistic, the fn:concat() function requires two or more 
arguments. Also, the reference to xs:anyAtomicType seems odd: this 
abstract type doesn't seem to be present in RIF.

10) Section 4.11: We suspect there is a fourth difference between RIF 
Lists and XPath sequences: in RIF, there is no equivalence between an 
atomic value and a singleton list containing that value. (Otherwise, 
pred:is-list() would be meaningless).

11) Section 4.11.1. Is it wise to number positions in a list starting 
from zero, while numbering characters within a string (for example, 
in the substring() function) from 1?  We think this inconsistency 
will confuse your readers and users.

12) Section There is no function fn:union. The link is to 
op:union, but the RIF function is essentially unrelated to op:union, 
as it is defined on atomic values rather than nodes. Same applies to fn:intersect and fn:except. XPath contains no 
functions to manipulate sequences of atomic values in this way: such 
functions can easily be written by users as explained in F+O appendix E.2.

13) Section it's not clear what "in the same order" means. 
Order of first appearance, perhaps?

14) In various places in section 4, we read phrases such as "the 
value of the function is unspecified".  The discussion early in 
section 4 of that term states that implementations are free to do as 
they wish, including returning either true or false, as well as 
aborting evaluation of the containing expression/query.  In the specs 
for which we are responsible, as well as some well-known 
international standards, the term "implementation-dependent" is used 
for the same purpose.  You might consider the use of that term instead.

15) Near the beginning of section 2.3 and in Appendix 6, we see three 
places where an unexpected character (a hollow square box) appears.

Hope this helps,

Jim Melton --- Editor of ISO/IEC 9075-* (SQL)     Phone: +1.801.942.0144
   Chair, W3C XML Query WG; XQX (etc.) editor       Fax : +1.801.942.3345
Oracle Corporation        Oracle Email: jim dot melton at oracle dot com
1930 Viscounti Drive      Standards email: jim dot melton at acm dot org
Sandy, UT 84093-1063 USA          Personal email: jim at melton dot name
=  Facts are facts.   But any opinions expressed are the opinions      =
=  only of myself and may or may not reflect the opinions of anybody   =
=  else with whom I may or may not have discussed the issues at hand.  =
Received on Friday, 25 September 2009 01:05:25 UTC

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