rdblue commented on code in PR #10835:
URL: https://github.com/apache/iceberg/pull/10835#discussion_r1700680980


##########
format/spec.md:
##########
@@ -241,7 +241,13 @@ Struct evolution requires the following rules for default 
values:
 
 #### Column Projection
 
-Columns in Iceberg data files are selected by field id. The table schema's 
column names and order may change after a data file is written, and projection 
must be done using field ids. If a field id is missing from a data file, its 
value for each row should be `null`.
+Columns in Iceberg data files are selected by field id. The table schema's 
column names and order may change after a data file is written, and projection 
must be done using field ids.
+
+Values for Field ids which are not present in a data file must be resolved 
according the following rules:
+
+* Return the value from partition metadata if an [Identity 
Transform](#partition-transforms) exists for the field. 

Review Comment:
   > Return the value from partition metadata if the data file's partition 
metadata contains the field as a result of the `identity` transform.
   
   I want to be clear that this is only required if the data file's partition 
metadata contains the field, not just if there is a partition spec that uses an 
identity transform for the field.



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