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

["Liam R. E. Quin" <liam@w3.org>]

On Thu, 2015-04-30 at 15:50 +0000, Costello, Roger L. wrote:
> Thank you for the fantastic feedback!
> 
> I updated the list using your feedback. Is there anything else that 
> should be added?  /Roger
> 
> --------------------------------------
> 
> JSON is often compared to XML. However, there are significant 
> differences:
> -          XML supports comments, JSON does not.
> -          XML supports processing instructions, JSON does not.
> -          XML provides multiple syntaxes to express things (e.g., 
> attribute values can be delimited by either a single or double 
> quote, attributes can be in any order), JSON does not have such 
> flexibility.

JSON has multiple ways to represent characters. For example,
a tab can be represented as \u0008 or \t or as a iteral tab.

> -          XML child nodes (text, elements, comments, PIs) have 
> order, the key/value pairs in JSON objects are unordered.
> -          XML uses canonicalization to convert XML into a standard 
> form. Since ordering doesn't exist in JSON objects, a canonical form 
> for JSON is problematic: with no canonical order, there's no 
> standard byte stream.
Ordering does exist in JSON array objects, and in strings of course.

One could define a canonical format for JSON; it would also have to 
take into account varying representations for characters in strings, 
equivalence of numeric strings and numbers in many applications, and 
of course whitespace between values.

> -          XML has namespaces, JSON does not.
> -          XML supports mixed content, JSON does not.
> -          XML has entities and notations, JSON does not.
> -          XML does not have arrays (although they can be 
> simulated),

This isn't really meaningful. XML is an information exchange language, 
where JSON is an object exchange language. XML files don't have 
objects, arrays, or even elements (just tags).

XML Schema has the ability to interpret text content as sequences of 
values, and XDM 3.1 (and XPath 3.1, XQuery 3.1) has arrays.

>  JSON has arrays. JSON objects inside arrays have position, but no 
> name; if an array is inside an object, then the name could be mapped 
> from the key name for the array member; JSON arrays inside arrays 
> inside an object are somewhat more of a challenge.
I don't understand why you feel nested objects are a challenge.

> -          XML uses different character sets (NCName) for markup 
> than for content, JSON uses the same character set throughout the 
> entire document.

"NCName" is not the name of a character set. It's a grammar production 
like { and } in JSON. So this is not really a difference.

> 
> -          XML supports any character encoding scheme, JSON supports 
> exclusively Unicode.
> -          XML has pointy brackets, JSON has curly and square ones.

The biggest differences I see are social:
(1) JSON formats are usually defined by developers to interchange or 
represent objects within a program: the developer is in control.
(2) XML is often used to represent information: the author is in 
control, not necessarily the developer.
(3) XML vocabularies are often constrained, e.g. with a grammar.
    If you add an extra item in a JSON object, in most cases
    non-one will notice or care.

Liam