Fast Infoset (FI) is a standard that can serve as an alternative to XML (Extensible Markup Language) document formatting. The FI specification, which was approved by the ITU (International Telecommunication Union) in May 2005 and published in March 2007, is designed to provide more efficient serialization than XML.
Documents in XML format can be converted to FI format and vice-versa without loss of content. In a simplified sense, FI documents resemble compressed XML documents. However, Fast Infoset optimizes the speed with which ASN.1 binary encoding is generated and processed and minimizes the file size. The FI specification defines encoding for an XML infoset, a data model consisting of up to 11 components known as:
- Document information items
- Document type declaration information items
- Character information items
- Notation information items
- Namespace information items
- Element information items
- Attribute information items
- Processing instruction information items
- Unexpanded entity reference information items
- Comment information items
- Unparsed entity information items.
The FI specification is also known as ITU-T Rec. X.891 and ISO-IEC 24821-1.