Re: [xml-dev] RE: List of differences between XML and JSON?

[Dimitre Novatchev <dnovatchev@gmail.com>]

This also explains the reason why a JSON object, similar to an XPath
3.1 map, doesn't have identity, while an XML document (or any other
node) has identity.

This makes a JSON object / map more efficient and easier to manipulate.

Remember that the identity rule (overridden to introduce some
modifications in the result, compared to the original XML document) is
by its complete-rewriting nature O(N). At the same time, with a good
map implementation producing a modified map from an existing one can
take O(log2(N)) or less.

Cheers,
Dimitre

On Fri, May 1, 2015 at 12:43 PM, Costello, Roger L. <costello@mitre.org> wrote:
> Below is a fantastic response from Walter Perry. Thank you Walter!  (Walter
> gave me permission to forward his message to the list)
>
> --------------------------------------
>
> The fundamental semantic premise of XML markup is the "hasA" relationship;
> that of JSON is "isA". This is the opposite of what one is likely to see at
> first blush, and it has taken me a full 20 years to understand how the
> syntax of XML enforces the "hasA" view, ultimately to the exclusion of
> "isA".
>
> Sparing the 20-year learning curve: the XML syntax permits only the
> expression of "hasA" relationships between entities--even where those
> 'entities' are expressed in the XML attribute syntax (color=blue means only
> that the enclosing entity *has* an identified color and that that color
> *has* the identified value 'blue'). The Generic Identifier itself of an XML
> entity expresses no more than that the entity *has* an identified label, and
> specifies its instance value. The axes of XSL are those along which the XML
> syntax permits the semantics of identified "hasA" relationships to be
> expressed.
>
> On the other hand, the semantically flat model of JSON allows the existence
> of anything to be naively induced if only it has a name:  use 'color' as a
> JSON name and presto, color exists as a nominal thing--and not merely as a
> Platonic form, but something immediately capable of instantiation in the
> real world as 'blue', 'red' or 'green'. Further, that color thing is
> implicitly global in scope, which is only another way of saying that the
> existence conferred upon 'color' by the "isA" semantic premise of JSON is an
> absolute existence. By contrast, such existence as we might posit for
> entities expressed in the XML syntax is contingent and scoped, and dependent
> ultimately on our willingness to make the leap of inductive reasoning
> required to conclude that we have a sufficient number of specific "hasA"
> relationships from which we may imagine a generic "isA" that types them.
>
> This is why JSON cannot have meaningful namespaces:  semantics which rely on
> the primacy of "isA" do not then permit that existence to be scoped and made
> contingent upon "hasA" relationships. And--whatever one might think of the
> specific W3C-anointed syntax for XML namespaces--the semantics expressed
> through the XML syntax are the very essence of namespacing. Every XML entity
> is, or is potentially, both containing and contained by "hasA"
> relationships. It's namepaces all the way down--which is to say, scoped and
> contingent existence.
>
> Respectfully,
>
> Walter Perry