Ion (serialization format)

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Filename extension
Internet media typeapplication/ion
Developed byAmazon
Type of formatData interchange

Ion is a data serialization language developed by Amazon. It may be represented by either a human-readable text form or a compact binary form. The text form is a superset of JSON; thus, any valid JSON document is also a valid Ion document.

Data types[edit]

As a superset of JSON, Ion includes the following data types

  • null: An empty value
  • bool: Boolean values
  • string: Unicode text literals
  • list: Ordered heterogeneous collection of Ion values
  • struct: Unordered collection of key/value pairs

The nebulous JSON 'number' type is strictly defined in Ion to be one of

  • int: Signed integers of arbitrary size
  • float: 64-bit IEEE binary-encoded floating point numbers
  • decimal: Decimal-encoded real numbers of arbitrary precision

Ion adds these types:

  • timestamp: Date/time/time zone moments of arbitrary precision
  • symbol: Unicode symbolic atoms (aka identifiers)
  • blob: Binary data of user-defined encoding
  • clob: Text data of user-defined encoding
  • sexp: Ordered collections of values with application-defined semantics

Each Ion type supports a null variant, indicating a lack of value while maintaining a strict type (e.g.,, null.struct).

The Ion format permits annotations to any value in the form of symbols. Such annotations may be used as metadata for otherwise opaque data (such as a blob).



Sample document[edit]

// comments are allowed in Ion files using the double forward slash 
  key: "value",   // key here is a symbol, it can also be a string as in JSON
  nums: 1_000_000, // equivalent to 1000000, use of underscores with numbers is more readable
  'A float value': 31415e-4,  // key is a value that contains spaces 
  "An int value": .int,
  annotated: age::35,     // age here is the annotation to number 35
  lists : 'hw grades'::[80, 85, 90], // any symbol can be used as an annotation 
  many_annot: I::have::many::annotations::true, // annotations are not nested, but rather, a list of annotations
  sexp: (this (is a [valid] "Ion") last::value 42) // Ion S-expressions, 
  _value: {{OiBTIKUgTyAASb8=}},
  _value: {{"a b"}}


  • Amazon's Quantum Ledger Database (QLDB) stores data in Ion documents.[1]
  • PartiQL, an open source SQL-based query language also by Amazon, is built upon Ion. PartiQL supported queries are used by QLDB, S3Select.[2]

Tooling and extensions[edit]


  1. ^ "We are the Amazon Managed Blockchain and Amazon QLDB Teams – Ask the AWS Experts – November 29 @ 3PM PST / 6PM EST". 28 November 2018.
  2. ^ "Announcing PartiQL: One query language for all your data". August 2019.

External links[edit]