Binary XML (EXI) Last Call

By Erik Wilde
September 22, 2008 | Comments: 1

On September 19, the W3C published the Last Call Working Draft for Efficient XML Interchange (EXI). Like many other XML technologies, it is not really about XML, it is about an efficient binary representation for Infosets, which are the data model underlying most XML technologies. Basically, EXI allows XML-based implementations to efficiently exchange documents, without having to use XML's verbose character-based syntax. Here's the abstract:

This document is the specification of the Efficient XML Interchange (EXI) format. EXI is a very compact representation for the Extensible Markup Language (XML) Information Set that is intended to simultaneously optimize performance and the utilization of computational resources. The EXI format uses a hybrid approach drawn from the information and formal language theories, plus practical techniques verified by measurements, for entropy encoding XML information. Using a relatively simple algorithm, which is amenable to fast and compact implementation, and a small set of data types, it reliably produces efficient encodings of XML event streams. The event production system and format definition of EXI are presented.

The Web supports the concept of transfer encodings with HTTP's concept of transfer codings and the Transfer-Encoding header field. In the same way as today's browsers can reliably process gzip'ed Web pages, future XML implementations will be able to dynamically agree on using EXI as transfer encoding (once it is registered with IANA as a well-known transfer encoding), thus greatly minimizing the amount of network bandwidth required for transmitting XML.

Last Call drafts in W3C-land mean that the working group considers the draft to be ready to be released as a recommendation. This means this is the last opportunity to submit comments about this document before it will be considered for publication as a recommendation.

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1 Comment


Thank you for raising awareness of EXI! Those interested in taking EXI for a spin, can download free evaluation copies of EXI products from These include support for content negotiation via HTTP transfer encoding as you described above. Feedback is always appreciated!


John Schneider
Editor, EXI specification
CTO, AgileDelta, Inc.

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