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Fast Infoset

ITU-T X.891 | ISO/IEC 24824-1 (Fast Infoset) specifies a representation of an instance of the W3C XML Information Set using binary encodings. These binary encodings are specified using the ASN.1 notation and the ASN.1 Encoding Control Notation (ECN). The Fast Infoset standard can be downloaded for free from the ITU-T website.

The Fast Infoset technology provides an alternative to W3C XML syntax as a means of representing instances of the W3C XML Information Set. This representation generally provides smaller encoding sizes and faster processing than a W3C XML representation.

Fast Infoset specifies the use of several techniques that minimize the size of the encodings (called fast infoset documents) and that maximize the speed of creating and processing fast infoset documents. These techniques include the use of dynamic tables (for both character strings and qualified names), initial vocabularies, and external vocabularies.

Some compression results are published by the open source Fast Infoset project (parsing performance, size performance). Note that these tests don't use any of the so-called Fast Infoset advanced features which allow for the use of external information (e.g., schema) to employ better representations for "text" nodes (e.g., IEEE float for xsd:float, etc.). Using those features, the performance gains can be significantly better

The ASN.1 Schema for the XML information set provides the capability to encode XML content that is not described by a schema. It defines an alternative to XML 1.0 serialization and, like the ASN.1 Schema for SOAP, ensures the application of a consistent encoding technology.

Use cases

​Fast Infoset has been adopted by the Web3D community because it meets their requirements for the encoding of X3D documents.Here are some explicit use cases as documented by the W3C XML Binary Characterization (XBC) working group:

Other possible application domains are:

  • the Geography Markup Language (GML) as specified by OpenGIS;
  • the Airport Data Base (ADB) Subcommittee of Airlines Electronic Engineering Committee that will define a single open encoding formatfor airport data bases to be directly loaded in airborne systems, thus enhancing taxi operations;
  • the military space.
See also the thesis "Analysis of Binary XML Suitability for NATO Tactical Messaging" by Matthew E. Bayer (Sept. 2005).

In general Fast Infoset can be used when it is necessary to retain the XML property of self-description (or the structure) and one requires:

  • a boost to parsing speed; and
  • a moderate reduction in document size..

Fast Infoset security

​The ASN.1 Group has begun to work on a new ITU-T Recommendation | International Standard, entitled "Information Technology - Generic Applications of ASN.1 - Fast Infoset and Fast Web Services Security, that will specify the application of standard security methods to the Fast Infoset specification.

In order for applications to apply standard security methods to the Fast Infoset specification, it is necessary to specify transformations to be applied to fast infoset documents (or parts of them) to support the application of those security methods.

The scope of the work includes the following:
  • specification of a canonical form for fast infoset documents;
  • specification of an encryptable form for fast infoset documents;
  • use of a fast infoset document canonical form to support XML Signature Syntax and Processing for the signing of fast infoset documents or parts of them;
  • use of a fast infoset encryptable form to support XML Encryption Syntax and Processing for the encryption of fast infoset documents or parts of them.
ITU-T X.893 | ISO/IEC 24824-3 was approved on May 2007.