rdblue commented on a change in pull request #2654:
URL: https://github.com/apache/iceberg/pull/2654#discussion_r652201301
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File path: site/docs/spec.md
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@@ -176,6 +178,15 @@ Columns in Iceberg data files are selected by field id.
The table schema's colum
For example, a file may be written with schema `1: a int, 2: b string, 3: c
double` and read using projection schema `3: measurement, 2: name, 4: a`. This
must select file columns `c` (renamed to `measurement`), `b` (now called
`name`), and a column of `null` values called `a`; in that order.
+#### Identifier Field IDs
+
+A schema can optionally track the set of primitive fields that identify rows
in a table, using the property `identifier-field-ids` (see JSON encoding in
Appendix C).
+
+Two rows are the "same"---that is, the rows represent the same entity---if the
identifier fields are equal. However, uniqueness of rows by this identifier is
not guaranteed or required by Iceberg because it is needlessly inefficient in
some cases. Reasonable steps to enforce uniqueness are the responsibility of
processing engines.
Review comment:
Updated to use your suggested wording.
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