ISO-IEC 24821-1

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What Does ISO-IEC 24821-1 Mean?

ISO-IEC 24821-1 is an international standard, which specifies a format for XML documents. It defines a standard for interpreting the XML information set (XML Infoset) with the help of binary encoding. The ASN.1 and ASN.1 Encoding Control Notation (ECN) are the widely used notations for specifying binary encodings.


This term is also known as Fast Infoset (FI).

Techopedia Explains ISO-IEC 24821-1

The ISO-IEC 24821-1 was released in 2007 as a technology based standard. It was then called Fast Infoset. The FI technology was developed as a substitute to World Wide Web Consortium (W3C) XML syntax. The FI specification is approved by the International telecommunication Union (ITU) and was first published in May 2005 by ITU and then by ISO in 2007. The FI specification was approved by both ITU and ISO. The FI technology unfolds several techniques, which help to reduce the size of the encodings. It also helps to achieve faster processing of documents when compared to the W3C XML representation. The documents created in XML format can be converted into FI format very easily. Another myth about FI ASN.1 is that FI requires ASN.1 tool support. Though FI specifications are based on ASN.1 notations, FI does not require ASN.1 tools in actual implementation.

ISO/IEC 24824-1 allows the use of dynamic tables (for representing both character strings and qualified names) and initial and external vocabularies.

ISO/IEC 24824-1 also defines a multipurpose Internet mail extensions (MIME) media type, which recognizes an FI document. The FI specification depends on ASN.1 file format. It may include tag/length/value blocks. Length prefixers are used instead of delimeters to store text values of attributes and elements.

Fast Infosets are usually compressed during the XML file generation process. This makes them even faster when compared to Zip-style compression algorithms on an XML stream. The performance of FI is much faster with simple API (application programming interface) for XML (SAX) type parsing when compared to the parsing performance of XML 1.0 without Zip-style compression.

Some of the advantages of ISO-IEC 24821-1 are as follows:

  • There are no end tags. The character duplication for end tags become unnecessary.
  • No characters are escaped. Character checking can consume time. If any character needs to be replaced, it may result in additional time and memory usage.
  • The use of length-prefixers for content allows a decoder to allocate resources accurately. Large content can be rejected immediately.
  • The repeated strings are indexed. This helps minimize document size. The repeated string is replaced by a commonly used string with an integer. Examples include element and attribute names.

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Margaret Rouse
Technology Expert
Margaret Rouse
Technology Expert

Margaret is an award-winning technical writer and teacher known for her ability to explain complex technical subjects to a non-technical business audience. Over the past twenty years, her IT definitions have been published by Que in an encyclopedia of technology terms and cited in articles by the New York Times, Time Magazine, USA Today, ZDNet, PC Magazine, and Discovery Magazine. She joined Techopedia in 2011. Margaret's idea of a fun day is helping IT and business professionals learn to speak each other’s highly specialized languages.