etseidl commented on code in PR #466:
URL: https://github.com/apache/parquet-format/pull/466#discussion_r1827257237
##########
LogicalTypes.md:
##########
@@ -648,49 +650,92 @@ optional group my_list (LIST) {
}
```
-Some existing data does not include the inner element layer. For
-backward-compatibility, the type of elements in `LIST`-annotated structures
-should always be determined by the following rules:
+##### 2-level structure
+
+Some existing data does not include the inner element layer, meaning that
`LIST`
+annotates a 2-level structure. In contrast to 3-level structure, the repetition
+of 2-level structure can be `optional`, `required`, or `repeated`.
+
+```
+<list-repetition> group <name> (LIST) {
+ repeated <element-type> <element-name>;
+}
+```
+
+For backward-compatibility, the type of elements in `LIST`-annotated 2-level
+structures should always be determined by the following rules:
1. If the repeated field is not a group, then its type is the element type and
elements are required.
-2. If the repeated field is a group with multiple fields, then its type is the
- element type and elements are required.
-3. If the repeated field is a group with one field and is named either `array`
- or uses the `LIST`-annotated group's name with `_tuple` appended then the
- repeated type is the element type and elements are required.
-4. Otherwise, the repeated field's type is the element type with the repeated
- field's repetition.
+2. If the repeated field is a group with multiple fields, then its type (Struct
+ type with multiple fields) is the element type and elements are required.
+3. If the repeated field is a group with one `required` or `optional` field,
+ and is named either `array` or uses the `LIST`-annotated group's name with
+ `_tuple` appended, then the repeated type (Struct type with single field) is
+ the element type and elements are required.
+4. If the repeated field is a `LIST`-annotated group with one `repeated` field,
Review Comment:
Got it, thanks.
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