fn:xml-to-json: Amendments

[ChristianGruen]

Maybe I was too quick in waving through #1476 as I believe that the current version is a bit sketchy. It says:

An element $E named number is processed by copying the string value of $E to the output, making any changes that are necessary to ensure that the result is a valid JSON number. Such changes include:

• Removing leading and trailing whitespace.
• Removing a leading plus sign.
• Removing redundant leading zero digits.
• Adding a zero digit before or after a decimal point that is not preceded and followed by a digit.

1. For input like X, we cannot ensure that it will be a valid JSON number, so I assume that the changed string needs to be validated before being output?
2. “Removing redundant leading zero digits” may not consider negative number like -01.
3. Does “Such changes include” imply that the list may not be comprehensive?

In many cases, the numbers to be output will be the result of an earlier json-to-xml conversion. If it is generated with XPath numbers, we shouldn’t encounter plus signs, redundant leading zeros etc. either, so I would suggest getting rid of all post-processing. We could simply say:

An element $E named number results in the output of the string value of the element if it is a valid JSON number. Otherwise, [FOJS0006] is raised.

If we do want to tweak the string value, we should provide a complete set of rules; maybe something like…

The string value of an element $E named number is modified by:

• removing leading and trailing whitespace,
• removing a single leading plus sign,
• removing redundant leading zero digits, which are optionally preceded by a leading minus sign,
• adding a zero digit before a decimal point that is not preceded by a digit, and
• adding a zero digit after a decimal point that is not followed by a digit.

If the result is a valid JSON number, it is output. Otherwise, [FOJS0006] is raised.

…but that’s still fuzzy (for example, it lacks the explanation of what redundant zero digits are).

[ChristianGruen]

Adding a zero digit before or after a decimal point that is not preceded and followed by a digit.

I just wondered if a . input string should really be replaced by 0.0?
I think we should drop all cleanups.

[michaelhkay]

Actually, I deliberately left the rules a bit fuzzy, because I wasn't 100% confident of getting them right. The key thing is that the result has to be valid JSON, and I gave a list of things you might need to do to ensure that; I worded it in such a way that if it turns out not to be a complete list of rules, the essential thing is that the result is valid JSON.

Note that there's already a constraint that the input must be a valid xs:double, so we don't have to deal with your example of .: the xs:double rules allow .1 and 1., but not .. We only have to deal with cases that are valid XML but not valid JSON.

I think we should drop all cleanups.

I disagree. If it's valid XML we should output valid JSON. That's what the function is for.

[ChristianGruen]

Note that there's already a constraint that the input must be a valid xs:double

I see; this is helpful information. So I assume the idea is that the original string should be validated first to be further modified by the rules, which convert an xs:double value to a correct JSON number?

I disagree. If it's valid XML we should output valid JSON. That's what the function is for.

I fully agree – but I think we should only validate the original string, without adjusting it by rules that may partially be implementation-dependent.