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Revisiting XML compression

In the most recent issue, we reported on how the Efficient XML Interchange (EXI) framework could cut back on the size of Extensible Markup Language-based event streams.

We stated that it was the only XML-compression standard, which, as it turns out, is wrong.

It was OSS Nokalva's Alessandro Triglia who corrected us on this matter. OSS Nokalva has a set of Fast Infoset tools.

Since Triglia who also had a lot interesting to say about Fast Infoset, and even made a few revealing comparisons with EXI, we'll reprint his e-mail here:

In your article you state that 'Many companies offer network appliances ...but no open standard has addressed this issue.' This is incorrect. Fast Infoset is an ISO standard (ISO/IEC 24824-1) which does precisely that, and was published in 2005 by both ISO/IEC and ITU. The standard is publicly available and can be downloaded for free from the ITU website.

It is a completely open standard which doesn't come with any royalties or patents or other encumbrances. There are open-source implementations as well as commercial implementations available. Implementation is relatively easy, as one of the design goals of this standard was ease of implementation.

Let me also point out that the statement in your article about EXI producing greater compression than Fast Infoset is not very meaningful as such, because such greater compression surely comes at the expense of something else. For example, there may be a cost in extra CPU cycles, or complexity of implementation, or stronger coupling between senders and recipients due to the need to share the schemas. Such stronger coupling may be problematic in many applications involving multiple loosely-connected systems.

Therefore, although it's true that EXI can achieve greater compression than Fast Infoset, many users will not be able to actually use EXI in such a way to enjoy that extra compression. In contrast, Fast Infoset is simple. It was designed to balance compression, speed, and ease of implementation. Moreover, it is a robust and proven international standard that has been
available for about three years.

We hear that the very idea of XML compression is heresy in some circles. The whole point of XML is that the data is plainly readable, so rendering it binary takes away its core strength. On the other hand, ASCI is an expensive way to carry data across the wire. In any case, it's always good to get more info on the topic.

Posted by Joab Jackson on Feb 08, 2008 at 9:39 AM


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