+This is a list of some of the known differences between the API here
+and the a1 spec dated 2019.09.30. In some cases, the spec is
+deficient and RIC is "ahead", in other cases this does not yet conform
+to recent spec changes.
+
+#. [RIC is ahead] There is no notion of policy types in the spec,
+ however this aspect is quite critical for the intended use of the
+ RIC, where many Xapps may implement the same policy, and new Xapps
+ may be created often that define new types. Moreover, policy types
+ define the schema for policy instances, and without types, A1
+ cannot validate whether instances are valid, which the RIC A1m
+ does. The RIC A1 Mediator view of things is that, there are a set
+ of schemas, called policy types, and one or more instances of each
+ schema can be created. Instances are validated against types. The
+ spec currently provides no mechanism for the implementation of A1
+ to know whether policy [instances] are correct since there is no
+ schema for them. This difference has the rather large consequence
+ that none of the RIC A1m URLs match the spec.
+#. [RIC is ahead] There is a rich status URL in the RIC A1m for policy
+ instances, but this is not in the spec.
+#. [RIC is ahead] There is a state machine for when instances are
+ actually deleted from the RIC (at which point all URLs referencing
+ it are a 404); this is a configurable option when deploying the RIC
+ A1m.
+#. [CR coming to spec] The spec contains a PATCH for partially
+ updating a policy instance, and creating/deleting multiple
+ instances, however the team agreed to remove this from a later
+ version of the Spec. The RIC A1m does not have this operation.
+#. [Spec is ahead] The RIC A1 PUT bodies for policy instances do not
+ exactly conform to the "scope" and "statements" block that the spec
+ defines. They are very close otherwise, however. (I would argue
+ some of the spec is redundant; for example "policy [instance] id"
+ is a key inside the PUT body to create an instance, but it is
+ already in the URL.)
+#. [Spec is ahead] The RIC A1m does not yet notify external clients
+ when instance statuses change.
+#. [Spec is ahead] The spec defines that a query of all policy
+ instances should return the full bodies, however right now the RIC
+ A1m returns a list of IDs (assuming subsequent queries can fetch
+ the bodies).
+#. [?] The spec document details some very specific "types", but the
+ RIC A1m allows these to be loaded in (see #1). For example, spec
+ section 4.2.6.2. We believe this should be removed from the spec
+ and rather defined as a type. Xapps can be created that define new
+ types, so the spec will quickly become "stale" if "types" are
+ defined in the spec.