Re: Action Item QT4CG-004-02: DN to make a proposal for deep-equal-safe for future discussion ( Re: Draft minutes for QT4CG meeting 004, 2022-09-27)

On Tue, Sep 27, 2022 at 11:41 PM Michael Kay <mike@saxonica.com> wrote:

> A couple of comments:
>
> (a) I have proposed (somewhere) changing the semantics of numeric
> comparisons using eq to convert both values to decimal rather than to
> double (as op:same-key does). But of course NaN=NaN would remain false.
> This function could take advantage of this.
>

Yes, certainly. Where?

>
> (b) The function inherits most of the weaknesses of fn:deep-equal. For
> example it's clearly a design mistake that comments and processing
> instructions are ignored without merging their adjacent sibling text nodes;
> the rules for comparing typed and untyped content are also pretty unusable,
> as is the treatment of whitespace. It's also unfortunate that fn:deep-equal
> gives a different result from serializing into XML canonical form and
> comparing the serializations. It's hard to know whether this matters
> without considering use cases for this new function; but if we're defining
> a new function, then we ought to fix the known faults in the old one.
>

The purpose of this function is not to correct design mistakes in
*fn:deep-equal*, but just to provide a function that can be used for
comparisons (such as of keys of maps even if maps could have any sequence
as a key)  that would return *false()* instead of raising errors, that
would be context-free and transitive. Another use case is to use it as a
possible default value for a *comparer* function arguments for any
functions that will need or benefit from having a comparer - argument.


>
> In practice I don't think it's possible to define a set of rules for
> comparing node trees that satisfies a wide range of use cases without
> parameterising it. Even the rules for canonical XML are parameterized
> (IIRC) in regards to their handling of namespaces and whitespace.
>

Yes, and we can choose a set of default values for these parameters to be
used in a *default-comparer-function*. These two ideas are complementary to
each other, not in conflict with each other.


>
> So it boils down to: what are the use cases that this new function is
> designed for?
>

As mentioned above. And any use-case for the separately/independently
proposed, and included by you in the PDF checklist document, *deep-equal
with options*, is also a use case for providing this function as a
*default-comparer*.


>
> Michael Kay
>


Thanks,
Dimitre


>
>
> On 28 Sep 2022, at 04:17, Dimitre Novatchev <dnovatchev@gmail.com> wrote:
>
>
>
> On Tue, Sep 27, 2022 at 9:42 AM Norm Tovey-Walsh <norm@saxonica.com>
> wrote:
>
>>
>>
>> Draft Minutes
>>
>> Summary of new and continuing actions [0/7]
>>
>>      * [ ] QT4CG-002-01: NW to incorporate email feedback and produce new
>>        versions of the process documents.
>>      * [ ] QT4CG-003-03: NW to tweak the CSS for function signatures to
>> avoid
>>        line breaks on - characters.
>>      * [ ] QT4CG-002-10: BTW to coordinate some ideas about improving
>>        diversity in the group
>>      * [ ] QT4CG-004-01: MK (with DN and RD) to draft a new proposal for
>>        variadic functions
>>      * [ ] QT4CG-004-02: DN to make a proposal for deep-equal-safe for
>> future
>>        discussion
>>      * [ ] QT4CG-004-03: MK to draft a pull request implementing
>>        fn:intersperse
>>      * [ ] QT4CG-004-04: DN to open an issue for the inverse of
>>        fn:intersperse
>>
>>
> The description of the function *fn:deep-equal-safe*() is in a pdf file
> that can be found here:
>
>
> *https://github.com/dnovatchev/FXSL-XSLT2/blob/master/fn-deep-equal-safe.pdf
> <https://github.com/dnovatchev/FXSL-XSLT2/blob/master/fn-deep-equal-safe.pdf>*
> Note: this document is essentially a compilation from the FO 3.1 of:
>       *op:same-key*  (
> https://www.w3.org/TR/xpath-functions-31/#func-same-key),  and
>       *fn:deep-equal *(
> https://www.w3.org/TR/xpath-functions-31/#func-deep-equal)
>
> Special care was taken to substitute the fn:deep-equal semantics that
> either results in raising an error, or in possible intransitivity or
> context-dependency. All such behavior has been substituted with the
> corresponding behavior from *op:same-key*, which the 3.1 Spec claims to
> be: "*deterministic, context-independent, and ·focus-independent*", etc.
>
> More specifically, to achieve this:
>
>
>    1. No errors are raised, instead *false() *is returned
>
>    2. Strings are compared without any dependency on collations (*fn:codepoint-equal
>    *is used in such comparisons)
>
>    3. Not using *eq *but instead every instance of *xs:double, xs:float
>    and xs:decimal* is represented exactly as a decimal number provided
>    enough digits are available both before and after the decimal point.Unlike
>    the *eq  *relation which converts both operands to *xs:double* values,
>    possibly losing precision in the process, this comparison is transitive
>
>    4. *fn:deep-equal* is used in comparing values having a variety of
>    date, time, year, month day types so that, unlike when using *eq*, no
>    error is raised when comparing values of different types, but just
>    *fasle()* is returned. Also, unlike when using the *eq *operator, this
>    comparison has no dependency on implicit time-zone, meaning no dependency
>    on this aspect of the dynamic context.
>
>
> The goal of this function description is to serve as a starting point for
> discussion about possible options for fn:deep-equal.
>
> Any comments will be appreciated.
>
> Thanks,
> Dimitre
>
>
>

-- 
Cheers,
Dimitre Novatchev
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