Efficient XML Interchange

Efficient XML Interchange (EXI) is a binary XML format for exchange of data on a computer network. It was developed by the W3C's Efficient Extensible Interchange Working Group and is one of the most prominent binary XML efforts to encode XML documents in a binary data format, rather than plain text. Using EXI format reduces the verbosity of XML documents as well as the cost of parsing. Improvements in the performance of writing (generating) content depends on the speed of the medium being written to, the methods and quality of actual implementations.

The World Wide Web Consortium (W3C) formed a working group to standardize on a format in March 2006. EXI was chosen as W3C's Binary XML format after an evaluation of various proposals that included Fast Infoset. EXI was adopted as a W3C recommendation by the W3C on 10 March 2011. A second edition was published in February 2014.

EXI was recommended for use in the US Department of Defense Global Information Grid.

In November 2016, the working group was renamed to "Efficient Extensible Interchange (EXI)" from "Efficient XML Interchange (EXI)" to reflect the broader scope of EXI applicability.

The EXI format is derived from the AgileDelta Efficient XML format.

An advantage of EXI over Fast Infoset is that EXI (optionally) uses more constraints from the XML schema. This can make the EXI data more compact; for example, if the XML schema specifies that elements named 'bar' may only exist within elements named 'foo', EXI can assign a shorter token to the 'bar' element, knowing that it doesn't have to share the same token space as elements that occur elsewhere in the document.

The main disadvantage is that to take advantage of this "schema-informed" compression, not only does the document require a schema, but the decoder needs a copy of the same schema that the encoder used.

EXI4JSON is a specification developed by the same working group to use the same format for JSON documents.

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