Versioning
==========

As the Corda platform evolves and new features are added it becomes important to have a versioning system which allows
its users to easily compare versions and know what feature are available to them. Each Corda release uses the standard
semantic versioning scheme of ``major.minor.patch``. This is useful when making releases in the public domain but is not
friendly for a developer working on the platform. It first has to be parsed and then they have three separate segments on
which to determine API differences. The release version is still useful and every MQ message the node sends attaches it
to the ``release-version`` header property for debugging purposes.

It is much easier to use a single incrementing integer value to represent the API version of the Corda platform, which
is called the Platform Version. It is similar to Android's `API Level <https://developer.android.com/guide/topics/manifest/uses-sdk-element.html>`_.
It starts at 1 and will increment by exactly 1 for each release which changes any of the publicly exposed APIs in the
entire platform. This includes public APIs on the node itself, the RPC system, messaging, serialisation, etc. API backwards
compatibility will always be maintained, with the use of deprecation to migrate away from old APIs. In rare situations
APIs may have to be removed, for example due to security issues. There is no relationship between the Platform Version
and the release version - a change in the major, minor or patch values may or may not increase the Platform Version.

The Platform Version is part of the node's ``NodeInfo`` object, which is available from the ``ServiceHub``. This enables
a CorDapp to find out which version it's running on and determine whether a desired feature is available. When a node
registers with the Network Map Service it will use the node's Platform Version to enforce a minimum version requirement
for the network.

.. note:: A future release may introduce the concept of a target platform version, which would be similar to Android's
   ``targetSdkVersion``, and would provide a means of maintaining behavioural compatibility for the cases where the
   platform's behaviour has changed.