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CDCBitMapExpansionExample/README.md

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+# Pub/Sub API Example - Change Data Capture Bitmap Expansion
+
+Because the Pub/Sub API is a binary API, delivered events are formatted as raw
+Avro binary and sometimes contain fields that are not plaintext-readable. This
+manifests in Change Data Capture events, causing them to look different from
+how they are delivered when subscribing via Streaming API. 
+
+For example, a Change Data Capture  event received via Pub/Sub API might look
+like this:
+
+```
+{'ChangeEventHeader': 
+	{
+		...
+		'nulledFields': [],
+		'diffFields': [],
+		'changedFields': ['0x650004E0']
+	},
+ ...
+}
+```
+
+In this example, `changedFields` is encoded as a bitmap string. This method is
+more space efficient than using a list of field names. A bit set to 1 in the
+`changedFields` bitmap value indicates that the field at the corresponding
+position in the Avro schema was changed. More information about bitmap fields
+can be found under "Bitmap Fields in Change Events" in the [onboarding
+guide](https://resources.docs.salesforce.com/rel1/doc/en-us/static/pdf/Salesforce_Pub_Sub_API_Pilot.pdf).
+
+We have provided this example to demonstrate how bitmap values can be decoded
+so that they are human-readable and you can process the event by using the
+values in the bitmap fields.