Canonical serialization

[Arithmeticus]

Canonical serialization

[michaelhkay]

(a) Yes I think it would be useful.

(b) I think my preference would be to use fn:serialize with method="canonical-xml". An alternative is to use method="xml" canonical="yes", but this has the disadvantage that there are many interactions with other serialization options, e.g. indent, cdata-section-elements, and omit-xml-declaration.

Note, if you want to experiment, Saxon already offers `method="xml" saxon:canonical="yes": see https://www.saxonica.com/documentation12/index.html#!extensions/output-extras/serialization-parameters. I tested this against the canonicalizer offered by XOM.

(c) There are certainly users who would want XML Signature for document signing, rather than just canonicalisation.

[ChristianGruen]

I also think this would be useful.

(b) I think my preference would be to use fn:serialize with method="canonical-xml". An alternative is to use method="xml" canonical="yes", but this has the disadvantage that there are many interactions with other serialization options, e.g. indent, cdata-section-elements, and omit-xml-declaration.

+1 for adding a custom method, and we should raise an error if the input is not a single node.

[Arithmeticus]

In thinking about discussion that might happen on this issue at today's CG meeting, I noted to myself:

• CX1.1 has a boolean parameter for whether comments are significant.
• CX1.1 resolves not to normalize namespace prefixes or characters.
• Some options in the options map of fn:serialize express parameters one might like to adjust in canonical serialization.
• Most of the options in the options map in fn:deep-equal express even more parameters one might like to adjust in canonical serialization, including namespace prefixes and characters.
• There is overlap between the two abovementioned functions' options maps, with some inconsistency, e.g., undeclare-prefixes versus namespace-prefixes.
• The default setting for namespace-prefixes in the map options for fn:deep-equal runs against CX1.1's resolution.

Ideas for a way forward to avoid repetition in the specs:

• Identify a common set of options from fn:deep-equal and fn:serialize that should apply to canonical serialization.
• From the common set, define a canonical serialization options map that can be referred to by both functions, or any other function that might need to appeal to canonical serialization options. Where names, behavior, or default of options in fn:deep-equal and fn:serialize conflict, let the latter prevail (in XQFO 3.1 fn:deep-equal lacks an options map).
• Introduce and describe that options map in its own section, structured analogous to what already exists for the regular expression functions. That is, refer to the external standard being used, CX1.1, but specify where adjustments have been made.

I am uncertain what edits might be needed to the serialization specs, particularly for those options in fn:deep-equal that have no fn:serialize counterpart, e.g., schema-aware adjustments, processing-instructions. It may turn out we wish not to include some of these in a common options map. Let's discuss.