szehon-ho commented on code in PR #16972: URL: https://github.com/apache/iceberg/pull/16972#discussion_r3484557395
########## format/spec.md: ########## @@ -345,6 +346,33 @@ For example, a struct column `point` with fields `x` (default 0) and `y` (defaul Default values are attributes of fields in schemas and serialized with fields in the JSON format. See [Appendix C](#appendix-c-json-serialization). +#### Collations + +A `string` field may carry a **collation**, an attribute that changes how the field's values are compared and ordered without changing how they are stored. Collations enable case-insensitive, accent-insensitive, and locale-aware comparison and sorting. A collation only affects comparison: the stored value is returned unchanged (a value written as `'appLE'` is read back as `'appLE'`). + +A field's collation is stored as a `collation` attribute on the field (see [Appendix C](#appendix-c-json-serialization)). The attribute is allowed only on `string` fields. If a field has no `collation` attribute, comparison defaults to UTF-8 byte order, which is the behavior of all prior versions. + +A collation is identified by a provider-qualified name of the form `<provider>.<name>`, for example `icu.en_US-ci`. The provider names the library that defines the collation (`icu` for collations defined by the [Unicode Collation Algorithm](https://unicode.org/reports/tr10/) over [CLDR](https://cldr.unicode.org/) locale data; other providers may define engine-specific collations such as case-folding variants). The name selects a locale and optional modifiers for case sensitivity (`ci`/`cs`), accent sensitivity (`ai`/`as`), trimming, and case folding. The reserved name `utf8` denotes UTF-8 byte-order comparison. + +The schema stores the collation **name without a version**, so any engine that supports the collation can read the table. UCA, DUCET, CLDR, and ICU collation orders are [not stable across versions](https://unicode.org/reports/tr10/#Non-Goals), so collation-aware metrics carry the implementation version they were produced under (see below) and a reader uses them only when it can produce the same order. Review Comment: nit: its describing too much about bounds which is already covered below? Also 'can read the table' is a bit vague as it should be read without stats-pruning, so suggest remove how about just a reference: `The schema stores the logical collation name without a version. Collation-aware file metrics store the implementation version used to compute their bounds (see below)` -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. To unsubscribe, e-mail: [email protected] For queries about this service, please contact Infrastructure at: [email protected] --------------------------------------------------------------------- To unsubscribe, e-mail: [email protected] For additional commands, e-mail: [email protected]
