added general rule on monitoring APIs and renamed api-discovery chapt…

…er to api-operation

SUMMARY.md

@@ -17,7 +17,7 @@
 * [Common Headers](headers/CommonHeaders.md)
 * [Proprietary Headers](headers/ProprietaryHeaders.md)
 * [Deprecation](deprecation/Deprecation.md)
-* [API Discovery](api-discovery/ApiDiscovery.md)
+* [API Operation](api-operation/ApiOperation.md)
 * [Events](events/events.md)
 * [References](references/References.md)
 * [Tooling](tooling/Tooling.md)

api-operation/ApiOperation.md

@@ -1,4 +1,4 @@
-# API Discovery
+# API Operation
 
 ## {{ book.must }} Applications Must Provide Online Access to Their API (Swagger) Definitions
 
@@ -25,4 +25,11 @@ management.
 
 Further reading:
 
-* [Library to make your Spring Boot service crawlable via Twintip](https://github.com/zalando-stups/twintip-spring-web)
+* [Library to make your Spring Boot service crawlable via Twintip](https://github.com/zalando-stups/twintip-spring-web)
+
+## {{ book.should }} Monitor API Usage
+Owners of APIs used in production should monitor API service to get information about its using clients.
+This information, for instance, is useful to identify potential review partner for API changes.
+
+Hint: A preferred way of client detection implementation is by logging of the client-id retrieved from the OAuth token.
+

deprecation/Deprecation.md

@@ -38,7 +38,7 @@ section of the API definition.
 
 ## {{ book.must }} Monitor Usage of Deprecated APIs
 
-Owners of APIs used in production must monitor usage of deprecated APIs until the API can be shut down. Clients still using a deprecated API can be detected by logging the client-id retrieved via the OAuth token.
+Owners of APIs used in production must monitor usage of deprecated APIs until the API can be shut down in order to align deprecation and avoid uncontrolled breaking effects. See also the [general rule on API usage monitoring](../api-operation/ApiOperation.md)
 
 ## {{ book.should }} Add a Warning Header to Responses