Mike Beckerle
Architect, Scalable Computing
IBM Software Group
Information Integration Solutions
Westborough, MA
----- Forwarded by Mike Beckerle/Worcester/IBM on 05/24/2005 01:44 PM -----

ed.rice@hp.com

05/24/2005 01:26 PM

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Subject

TAG opinion on XML Binary Format

 
TAG opinion on XML Binary Format

The TAG has reviewed in detail the documents [1,2,3,4] prepared by the XBC
workgroup [5].  While we very much appreciate the significant progress that
these notes represent, the TAG believes that more detailed analysis is
needed before a W3C Binary XML Recommendation is sufficiently justified.  We
are taking no position at this time as to whether Binary XML will prove to
be warranted, as there seem to be good arguments on both sides of that
question.  Rather, we are suggesting that further careful analysis is needed
before the W3C commits to a direction.

The TAG believes there are disadvantages as well as potential advantages
that will result from even a well crafted Binary XML Recommendation.  The
advantages are clear: a successful binary format is likely to provide speed
gains or size reductions, at least for certain use cases.  The drawbacks are
likely to include reduced interoperability with XML 1.0 and XML 1.1
software, and an inability to leverage the benefits of text-based formats.
These are important concerns.  Quoting from the Web Architecture
document[6]:

  "The trade-offs between binary and textual data
  formats are complex and application-
  dependent. Binary formats can be substantially
  more compact, particularly for complex
  pointer-rich data structures. Also, they can be
  consumed more rapidly by agents in those cases
  where they can be loaded into memory and used
  with little or no conversion. Note, however,
  that such cases are relatively uncommon as such
  direct use may open the door to security issues
  that can only practically be addressed by
  examining every aspect of the data structure in
  detail.

  "Textual formats are usually more portable and
  interoperable. Textual formats also have the
  considerable advantage that they can be
  directly read by human beings (and understood,
  given sufficient documentation). This can
  simplify the tasks of creating and maintaining
  software, and allow the direct intervention of
  humans in the processing chain without recourse
  to tools more complex than the ubiquitous text
  editor. Finally, it simplifies the necessary
  human task of learning about new data formats;
  this is called the "view source" effect."

We therefore believe that the benefits of a binary XML must be predictable
and compelling in order to justify development of a Recommendation.

In particular, we suggest that a quantitative analysis is necessary.  For at
least a few key use cases, concrete targets should be set for the size
and/or speed gains that would be needed to justify the disruption introduced
by a new format.  For example, a target might be that "in typical web
services scenarios, median speed gains on the order of 3x in combined
parsing and deserialization are deemed sufficient to justify a new format."
We further suggest that representative binary technologies be benchmarked
and analyzed to a sufficient degree that such speed or size improvements can
be reasonably reliably predicted before we commit to a Recommendation.  No
doubt, any given set of goals or benchmarks will suffer from some degree of
imprecision, but if the gains are sufficiently compelling to justify a new
format, then they should be relatively easy to demonstrate.  In short,
actual measurements should be a prerequisite to preparing a Recommendation.

In doing such measurements, we believe it is essential that comparisons be
done to the best possible text-based XML 1.x implementations, which are not
necessarily those that are most widely deployed.  Stated differently:
if XML 1.x is inherently capable of meeting the needs of users, then our
efforts should go into tuning our XML implementations, not designing new
formats.  Benchmark environments should be as representative as possible of
fully optimized implementations, not just of the XML parser, but of the
surrounding application or middleware stack.  We note that different
application-level optimizations may be necessary to maximize the performance
of the Binary or text cases respectively.  Care should especially be taken
to ensure that the performance of particular APIs such as DOM or SAX does
not obscure the performance possible with either option (e.g. both SAX and
DOM can easily result in high overhead string conversions when UTF-8 is
used.)

The TAG would also appreciate clarification as to how many formats are
likely to be included in a Recommendation; it's not clear whether the
proposal is for one binary xml format for all cases, or if multiple formats
are to be endorsed.  The use of multiple formats is likely to further reduce
interoperability.

We feel that introduction of a binary format would be an important
development for those who might benefit from its size or speed, but also for
those who might be impacted by its impact on interoperability and
perspicuity.  Therefore, in order to justify a potential new format, the TAG
would like to see the above issues addressed.  As stated above, we make no
prediction as to whether such an analysis will ultimately confirm the need
for Binary XML;  if it does, we will be glad to support development of a
Recommendation at the W3C.


[1]  http://www.w3.org/TR/xbc-use-cases/
<http://www.w3.org/TR/xbc-use-cases/>
[2]  http://www.w3.org/TR/xbc-properties/
<http://www.w3.org/TR/xbc-properties/>
[3]  http://www.w3.org/TR/xbc-measurement/
<http://www.w3.org/TR/xbc-measurement/>
[4]  http://www.w3.org/TR/xbc-characterization/
<http://www.w3.org/TR/xbc-characterization/>
[5]  http://www.w3.org/XML/Binary/ <http://www.w3.org/XML/Binary/>
[6]  http://www.w3.org/TR/webarch/#binary
<http://www.w3.org/TR/webarch/#binary>