On Mon, Aug 10, 2009 at 1:45 PM, Tom Lane<tgl@sss.pgh.pa.us> wrote:
> Robert Haas <robertmhaas@gmail.com> writes:
>> I may be thick as a post here and say "oh, I'm a moron" when you
>> explain this to me, but I still don't understand why that would
>> require the XML notation to interpose an intermediate node. Why can't
>> "filter" node itself can be the labelled container?
>
> Filter isn't a node; it's a property of the containing Plan node.
My use of the word node was poorly chosen, since that word has a
specific meaning in the context of PG.
> The way we have this set up, there's a distinction between properties
> and groups, which AFAICS we have to have in order to have directly
> comparable structures in XML and JSON. Didn't you design this
> yourself?
Yes, I did. But the point is that as far as I can see, the following
two things are equivalent:
<Filter><Text>(f1 > 0)</Text></Filter>"Filter": { "Text": "(f1 > 0)" }
And this is not:
<Filter><Expr><Text>(f1 > 0)</Text></Expr></Filter>
The latter would be equivalent to something like this in JSON:
"Filter" : { "Expr" : { "Text: "(f1 > 0)" } }
or if you intended the <Expr> thing to be an array-type container,
then it would be equivalent to this:
"Filter" : { [ { "Text: "(f1 > 0)" } ] }
Would it be helpful for me to try to reduce this to code?
> (I think part of the issue is that containers in JSON are anonymous
> whereas XML wants to assign them a named type. That's fine with me,
> in fact the JSON approach looks rather impoverished.)
That does make things a little tricky, though it has the virtue of
mapping nicely onto data structures other than XML.
...Robert