[ARROW-1587] [Format] Add metadata for user-defined logical types

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Fix Version/s: 0.14.0
• Component/s: Format
• External issue URL: https://github.com/apache/arrow/issues/17600
• Assignee: Wes McKinney
• Reporter: Wes McKinney
• Created: 20/Sep/17 23:59
• Updated: 11/Jan/23 07:15
• Resolved: 14/Jun/19 18:49

Description

While we have the custom_metadata field at the Field level, it may be useful to have a proper user-defined type metadata in the `Type` union, which would allow us to provide a physical representation type (e.g. "Latitude longitude is represented by a struct, whose children consist of two doubles") from the other non-user defined types.

This is more flexible than custom_metadata because we can leverage existing structure in the Flatbuffers for describing the user type

https://github.com/apache/arrow/blob/master/format/Schema.fbs#L285