Re: [xml-dev] Nested Documents (was: XML 2.0)

[Richard Salz <rsalz@us.ibm.com>]

> I don't understand what you mean by "more
tightly linked"...

In a single-rooted document, <a>...</a>,
when I see that final closing bracket I can be pretty sure that I've got
everything.  (Yes, trailing comments and PI's I handwave aside.)  If
the input stream ends before that closing bracket, then I know something
went wrong.  My XML consuming application can pretty much treat the
input as a stream of bytes and not care where how or why something went
wrong; at least at the first level.  See the bracket, things ok; don't
see the bracket, something broke.

Now, let's imagine a multi-rooted document like <a>...</a><b>...</b>.
 How do I know when I hit the end? Suppose the network drops after
the </a>?  If you're using something like TCP socket API, you
have no idea how many bytes were in-flight when the connection dropped.
 (TCP is realiable only when its working; it's failures modes are
pretty pitiful.)  Suppose I'm reading a log file and there's no free
space on the disk but I do see the closing </b>.  Is that coincidence
-- did the producer just get lucky and take the last bits of the disk,
or am I missing <c>...</c> and friends?

There's no way to know, in a generic way, without
doing very specific things depending on when where why and how the XML
is transported.  Right now, you don't have to.  Yes, that's a
simplification, 80/20, whatever you want to call it.  I'd call it
a trade-off and say the current design is the right one. :)

It has issues in the real world, too.  Suppose
you're writing a book and someone inserts a pagebreak between <a>
and <b> in a multi-root document.  Are they gonna get confused
or misled if they're not explicitly told to turn the page?

        /r$

--
STSM, DataPower Chief Programmer
WebSphere DataPower SOA Appliances
http://www.ibm.com/software/integration/datapower/