Tim's presentation is insightful.

Highlights (actually it's all good so this is most of the presentation):

Use plain text if... you possibly can.
JSON issues: Watch out for extensibility.
Use JSON if... The expected lifetime of the data is short.
Use XML if... your data is document flavoured or you're worried about i18n, extensibility or reusability.
Inventing New XML Languages:

Time-consuming.
Bureaucratic.
Difficult.
Unpleasant.
Includes complex software development as a sub-task.
Usually fails.
... so try not to!

Some Good XML Languages

XHTML
DocBook
ODF
Atom
XMPP
UBL
RDF

Design Issue: Model vs. Syntax

“What matters is getting the data model right. The syntax is ephemeral.” vs
“The bits on the wire are the only reality.”

Design Issue: Minimalism vs. Completeness

“Let’s solve the whole problem.”
“Minimum progress required to declare victory.”

XML Schema Definitions (XSD):

Hard to understand, hard to implement, hard to interoperate.
One of the reasons why the SOA/WS-* project is sinking.

XML Extensibility: Three Options

No changes.
Must-Understand policy (e.g. as in SOAP).
Must-Ignore policy (e.g. as in Atom).

Morals of the story (IMO):

Bend over backwards to use plain text (if we can)
JSON is more interesting for RPC than ROA (Resource Oriented Architecture)
Avoid inventing new [XML] languages at all costs
6 of the 7 "good" XML languages have already come up in the context of OCCI (NFI what UBL is)
Model and bits-on-the-wire are both important to us
RELAX NG and XPath is a GoodThing™
For XML extensibility ignore that which you don't understand (ala Atom)
Solve as much of the problem as we need to now but provide for extensibility later

Sam

---------- Forwarded message ----------
From: Tim Bray <tbray@textuality.com>
Date: 2009/5/27
Subject: Re: Structured data over TCP?
To: Patrik Fältström <patrik@frobbit.se>
Cc: apps-discuss@ietf.org

2009/5/26 Patrik Fältström <patrik@frobbit.se>:

> Do Apps Area have any general feeling about this?

I was going to start typing in a lengthy answer but then I remembered
I gave a tutorial at IETF70 on the choice of data formats for use in
Internet Protocols. It's centered around XML but I think covers many
of the other issues that have come up in this. Available for your
reading pleasure at http://www.tbray.org/tmp/IETF70.pdf

-Tim

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