Semantic Versioning Rationale (open-telemetry#232)

* Semantic Versioning Rationale

* Update docs/versioning.md

Co-authored-by: Daniel Dyla <[email protected]>

* Apply suggestions from code review

Co-authored-by: Daniel Dyla <[email protected]>

* Daniel Dyla Suggestions

Co-authored-by: Daniel Dyla <[email protected]>

README.md

@@ -93,3 +93,7 @@ The easy way to test the example out with docker and docker-compose is:
 3.) Go to Graph section, type "opentelemetry_prometheus_counter" in the search field or select it in the dropdown menu. You will see the counter value. Every other time you run `make metrics-prometheus-example` will increment the counter but remember that Prometheus scrapes values once in 10 seconds.
 
 4.) In order to stop docker containers for this example just run `make stop-prometheus`
+
+## Versioning
+
+Versioning rationale can be found in the [Versioning Documentation](/docs/versioning.md)

docs/versioning.md

@@ -0,0 +1,29 @@
+### Assumptions
+This project uses [semver v2](https://semver.org/), as does the rest of OpenTelemetry.
+
+### Goals
+#### API Stability:
+* Once the API for a given signal (spans, logs, metrics, baggage) has been officially released, that API module will function with any SDK that has the same major version and an equal or greater minor version.
+  * example: libraries that are instrumented with opentelemetry-api-trace:1.0.1 will function with SDK library opentelemetry-sdk-trace:1.11.33.
+* No existing method names or signatures will change with a patch release.
+* Method signatures may only change in a backwards compatible way with a minor release.
+
+#### SDK Stability:
+* Public portions of the SDK (constructors, configuration, end-user interfaces) must remain backwards compatible.
+* No existing public method names or signatures will change with a patch release.
+* Public method signatures may only change in a backwards compatible way with a minor release.
+
+### Methods
+#### Mature signals
+* Public portions of the SDK (constructors, configuration, end-user interfaces) must remain backwards compatible.
+* Internal interfaces are allowed to break.
+* API modules for mature (i.e. released) signals will be transitive dependencies of the OpenTelemetry API class.
+* Methods for accessing mature APIs will be added, as appropriate to the OpenTelemetry API interface.
+* SDK modules for mature (i.e. released) signals will be transitive dependencies of the SDK.
+* Configuration options for the SDK modules for mature signals will be exposed, as appropriate, on the OpenTelemetry SDK class.
+
+#### Immature or experimental signals
+* API namespaces for immature signals will not be transitive dependencies of the API class.
+* API namespaces will be named with an "-experimental" suffix to make it abundantly clear that depending on them is at your own risk.
+* The classes for immature APIs will be used as if they were mature signals. This will enable users to easily transition from immature to mature usage, without having to change imports.
+* SDK classes for immature signals will also be named with an "-experimental" suffix, in parallel to their API modules.