[GitHub] [beam] twang126 commented on a diff in pull request #26451: Add flexible windowing syntax to yaml.

["twang126 (via GitHub)" <gi...@apache.org>]

twang126 commented on code in PR #26451:
URL: https://github.com/apache/beam/pull/26451#discussion_r1180636363


##########
sdks/python/apache_beam/yaml/README.md:
##########
@@ -215,6 +215,157 @@ pipeline:
       path: /path/to/big.csv
 ```
 
+## Windowing
+
+This API can be used to define both streaming and batch pipelines.
+In order to meaningfully aggregate elements in a streaming pipeline,
+some kind of windowing is typically required. Beam's
+[windowing](https://beam.apache.org/documentation/programming-guide/#windowing)
+and [triggering](https://beam.apache.org/documentation/programming-guide/#triggers)
+can be be declared using the same WindowInto transform available in all other
+SDKs.
+
+```
+pipeline:
+  type: chain
+  transforms:
+    - type: ReadFromPubSub
+      topic: myPubSubTopic
+    - type: WindowInto
+      windowing:
+        type: fixed
+        size: 60
+    - type: SomeAggregation
+    - type: WriteToPubSub
+      topic: anotherPubSubTopic
+```
+
+Rather than using an explicit `WindowInto` operation, one may instead tag a
+transform itself with a specified windowing which will cause its inputs
+(and hence the transform itself) to be applied with that windowing.
+
+```
+pipeline:
+  type: chain
+  transforms:
+    - type: ReadFromPubSub
+      topic: myPubSubTopic
+    - type: SomeAggregation
+      windowing:
+        type: sliding
+        size: 60
+        period: 10
+    - type: WriteToPubSub
+      topic: anotherPubSubTopic
+```
+
+Note that the `Sql` operation itself often a from of aggregation, and applying

Review Comment:
   nit: maybe reword to `Note that the `Sql` operation itself  **is** often a from of aggregation, and applying a windowing ~which~ will cause all grouping to be done per window.` 



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