RussellSpitzer commented on code in PR #16425:
URL: https://github.com/apache/iceberg/pull/16425#discussion_r4418335279


##########
format/spec.md:
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@@ -1801,6 +1804,40 @@ If a delete column in an equality delete file is later 
dropped from the table, i
 
 Manifests hold the same statistics for delete files and data files. For delete 
files, the metrics describe the values that were deleted.
 
+### Column Files
+
+Starting in v4, a data file may store fields in column files listed in 
[`column_files`](#column-file-fields). A column file is an Iceberg data file 
and must have the same row count as its data file.
+
+A column file stores the entire value of each field in its `field_ids`. Each 
ID must identify a field in the table schema, or a row lineage field required 
by [Writing Column Files](#writing-column-files). A schema field must be 
top-level or nested in structs, must not be nested within a list or map, and 
must not be, or contain, a source field of the data file's partition spec.

Review Comment:
   "stores the entire value" is also a little confusing for me. 
   
   Maybe 
   |
   "A column file is responsible for all the values of the fields listed in 
it's `field_ids`"



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