serramatutu commented on code in PR #48002:
URL: https://github.com/apache/arrow/pull/48002#discussion_r2546657710
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docs/source/format/CanonicalExtensions.rst:
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@@ -544,6 +544,49 @@ Primitive Type Mappings
| UUID extension type | UUID |
+----------------------+------------------------+
+.. _timestamp_with_offset_extension:
+
+Timestamp With Offset
+=============
+This type represents a timestamp column that stores potentially different
timezone offsets per value. The timestamp is stored in UTC alongside the
original timezone offset in minutes.
+This extension type is intended to be compatible with ANSI SQL's ``TIMESTAMP
WITH TIME ZONE``, which is supported by multiple database engines.
+
+* Extension name: ``arrow.timestamp_with_offset``.
+
+* The storage type of the extension is a ``Struct`` with 2 fields, in order:
+
+ * ``timestamp``: a preferably non-nullable ``Timestamp(time_unit, "UTC")``,
where ``time_unit`` is any Arrow ``TimeUnit`` (s, ms, us or ns).
+
+ * ``offset_minutes``: a preferably non-nullable signed 16-bit integer
(``Int16``) representing the offset in minutes from the UTC timezone. Negative
offsets represent time zones west of UTC, while positive offsets represent
east. Offsets range from -779 (-12:59) to +780 (+13:00).
+
+* Extension type parameters:
+
+ * ``time_unit``: the time-unit of each of the stored UTC timestamps.
+
+* Description of the serialization:
+
+ Extension metadata is an empty string.
+
+.. note::
+
+ It is also *permissible* for the ``offset_minutes`` field to be
dictionary-encoded or run-end-encoded.
+
+.. note::
+
+ It is also *permissible* for ``timestamp`` and ``offset_minutes`` to be
nullable, but not recommended.
+
+ If ``timestamp`` is nullable and a value is found to be null, then the
whole ``TimestampWithOffset`` value should be interpreted as null. One way of
achieving this is to drop ``timestamp``'s validity buffer (V1) and replace the
top-level struct's validity buffer (V2) with the result of ``V1 AND V2``.
+
+ If ``offset_minutes`` is nullable and a value is found to be null, then
this value should be interpreted as if the offset value were were zero.
+
+ It is *recommended* that implementations normalize this type's
representation by dropping the inner validity buffers and applying the
aforementioned transformations, only keeping the top-level struct's validity
buffer.
+
+.. note::
Review Comment:
I added this mostly to make integrating to Arrow via JSON more ergonomic so
people can do stuff like `time.Parse()` in Go or `datetime.fromisoformat()` in
Python, instead of having to manually parse something like `{"timestamp":
"...", "offset": 123}` to get timezone-aware objects in their language.
I can take this off of the spec if you think it doesn't belong here though.
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