ajantha-bhat commented on code in PR #10280:
URL: https://github.com/apache/iceberg/pull/10280#discussion_r1593522217


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format/materialized-view-spec.md:
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+
+# Iceberg Materialized View Spec
+
+## Background and Motivation
+Iceberg views are a powerful tool to abstract complex queries and share them 
among different engines.
+However, such views are not materialized by default, which means that they are 
re-computed every time they are queried.
+This can be inefficient for complex queries that are computed frequently.
+Iceberg Materialized views are a way to store the results of an Iceberg view 
to reuse the computation in subsequent queries.
+
+## Goals 
+The goal of this spec is to define the metadata associated with materialized 
views in Iceberg.
+Such metadata allows creating and querying Iceberg materialized views across 
different engines.
+
+## Specification
+A materialized view is an Iceberg view with a respective Iceberg table that 
stores the results of the view query.
+An Iceberg view is considered a materialized view if it has the 
`materialized.view` property set to `true`.
+A materialized view must also reference the storage table identifier in its 
`materialized.view.storage.table` property.
+
+The specification for the materialized view properties on the view is as 
follows:
+| Property name                              | Description                     
                                        |
+|--------------------------------------------|-------------------------------------------------------------------------|
+| `materialized.view`                | This property is used to mark whether a 
view is a materialized view. If set to `true`, the view is treated as a 
materialized view.|
+| `materialized.view.storage.table`  | This property specifies the identifier 
of the storage table associated with the materialized view.|
+
+In addition to the properties on the view, the storage table associated with 
the materialized view has the following properties:
+
+| Property name                        | Description                           
                                        |
+|--------------------------------------|-------------------------------------------------------------------------------|
+| `base.snapshot.[UUID]`       | These properties store the snapshot IDs of 
the base tables at the time the materialized view's data was last updated. Each 
property is prefixed with `base.snapshot.` followed by the UUID of the base 
table.|
+| `view.version`               | This property stores the version of the view 
that this storage table is associated with at the time of materialization|
+| `child.view.version.[UUID]`  | If the top level materialized view is nested 
on top of other views, these properties store the version of the child views 
that the top level view is associated with at the time of materialization. Each 
property is prefixed with `child.view.version.` followed by the UUID of the 
child view.|
+
+A storage table is considered fresh if all the following conditions are true:
+* For each table `T` with `UUID` in `base.snapshot.[UUID]`, the current 
snapshot ID of `T` is equal to the value stored in `base.snapshot.[UUID]`.
+* The version of the view using the table as the storage table is equal to the 
value stored in `view.version`.
+* For each child view `V` with `UUID` in `child.view.version.[UUID]`, the 
version of `V` is equal to the value stored in `child.view.version.[UUID]`.

Review Comment:
   there is a chance that storage table of child views are outdated (not 
fresh). So, just comparing the view versions is not enough to conclude child 
views are fresh?



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