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+# Graph Taxonomy
+
+Different top-level segments have different requirements and these rules MUST be followed:
+
+* `/external`
+
+    * The `/external` top-level segment is used to expose data that is provided by third-party services.
+    * Microsoft Graph APIs that build on data or functionality provided by third-parties will want to reference the data from those third-parties.
+    The third-party data that is exposed on Microsoft Graph should be consistent with the data directly coming from the third-party services, but to be referenced by Graph APIs, CSDL entities need to be created and navigated to.
+    Doing this allows clients to have their data conveniently in a single API surface, while also maintaining consistency across the Microsoft Graph APIs and the third-party APIs.
+    * In addition to the first-party, scenario-based APIs, additional APIs should be released under the `/external` top-level segment.
+    The APIs under `/external` MUST not expose any data that is provided by Microsoft.
+    Any data that is available under `/external` MUST be data that could be retrieved directly from the third-party service; these APIs are only being added to Graph for convenience and interoperability.
+    * Microsoft Graph is not intended to be a single-pane-of-glass for all third-party APIs.
+    Only APIs that facilitate Graph scenarios should be exposed under `/external`.