Quoting Hans-Juergen Rennau
> Why would one want to apply XQuery concepts to JSON?
>
> Hence Dimitre's statement that in JSON subtrees can be shared makes (to me)
> only sense when equating JSON to a particular information model. (Which one?
> XDM maps/arrays? _javascript_ objects?)
Both XML and JSON instances are just a sequence of characters. This is it -- without adding to such a sequence of characters some more or less well-defined meaning. This meaning (semantics) can be quite formally defined -- as is the case with the XDM, or it may not have a formal definition, but still exist, defined by the common ways people use the language.
> But, but, but … the XDM is, as far as the XML specification is concerned, a fiction. That is, as far as the XML specification is concerned,
> all this XDM verbiage about nodes and
> trees and axes is pure fiction.
This is not a fiction, because this is the meaning people put behind the sequence of characters. It is the meaning, that is important -- there might be many different ways to express the same meaning, and we wouldn't care too much about the specific representation as long as it expresses the same meaning. It wouldn't be a "fiction" even if the sequence had meaning only to Martians... (ask the SETI folks ... :) )
So, my quoted statement above can be paraphrased into an equivalent statement: JSON is typically used to express a set of objects and the connections (links/edges) between them, without restricting how many links point to the same object. This makes JSON convenient for expressing directed graphs.
On the other hand, XDM formally defines one (and so far the most commonly used) meaning behind a syntactically-valid (as XML) sequence of characters:
- "Within a tree, document order satisfies the following constraints:
The root node is the first node.
Every node occurs before all of its children and descendants" ... etc. http://www.w3.org/TR/xpath-datamodel/#document-order
As we can see, according to this formally defined semantics, an XML document represents a document-node and this document node is the root of a tree
If we call this formal definition "a fiction", we could probably proclaim everything posted into this forum as "a fiction", and going further -- even the whole Internet and even anything represented in written form. The fact that you and I are reading this forum means that we probably disagree to perceive it as "a fiction".
So, Roger's question about "the differences between XML and JSON" isn't about the differences between two fictions -- it is about the differences of the meaning that the instances of these two languages are used to express.
Roger, could you please, agree or disagree with my understanding of the question?
--
Cheers,
Dimitre Novatchev
