Canonical Extension Types


The Arrow Columnar Format allows defining extension types so as to extend standard Arrow data types with custom semantics. Often these semantics will be specific to a system or application. However, it is beneficial to share the definitions of well-known extension types so as to improve interoperability between different systems integrating Arrow columnar data.


These rules must be followed for the standardization of canonical extension types:

  • Canonical extension types are described and maintained below in this document.

  • Each canonical extension type requires a distinct discussion and vote on the Arrow development mailing-list.

  • The specification text to be added must follow these requirements:

    1. It must define a well-defined extension name starting with “arrow.”.

    2. Its parameters, if any, must be described in the proposal.

    3. Its serialization must be described in the proposal and should not require unduly implementation work or unusual software dependencies (for example, a trivial custom text format or JSON would be acceptable).

    4. Its expected semantics should be described as well and any potential ambiguities or pain points addressed or at least mentioned.

  • The extension type should have one implementation submitted; preferably two if non-trivial (for example if parameterized).

Making Modifications

Like standard Arrow data types, canonical extension types should be considered stable once standardized. Modifying a canonical extension type (for example to expand the set of parameters) should be an exceptional event, follow the same rules as laid out above, and provide backwards compatibility guarantees.

Official List

No canonical extension types have been standardized yet.