rdblue commented on a change in pull request #3556:
URL: https://github.com/apache/iceberg/pull/3556#discussion_r749765084
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File path: site/docs/spec.md
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@@ -212,6 +212,33 @@ 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.
+Tables may also define a property `schema.name-mapping.default` with a JSON
`name mapping` containing a list of `field mapping` objects. These mappings
provide fallback field ids to be used when a data file does not contain field
id information. Each object should contain
+
+##### field mapping
+
+* `names`: A required list of 0 or more names for a field.
+* `field-id`: An optional Iceberg field ID used when a field's name is present
in `names`
+* `fields`: An optional list of field mappings for child field of structs,
maps, and lists.
+
+##### names
Review comment:
I don't think we need subsections for all of these. It should be easy
enough to read without them.
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