Query Service – Introduced in the vCloud 1.5 API. Useful when searching for resources. You do not have to traverse the resource tree to find specific children nodes. The query service has been expanded in the vCloud 5.1 API including the ability to query for metadata tags.

Metadata Tagging – Expanded in the vCloud 5.1 API. Annotate vCloud resources with typed metadata that can be system defined and either hidden from or read-only for users, or user defined that is read writable. Consumers can interact with metadata from the UI in vCloud Director 5.1; in previous releases, this feature is available only from the API.

API Extensions – New in the vCloud 5.1 API. Provides the ability to extend the vCloud API to modify existing functionality or to add new capabilities to the API.

Block Tasks and Notifications – Introduced in the vCloud 1.5 API. This feature relates to the messages published and consumed by vCloud Director. In blocking tasks, the system waits for a user to take an action. For example, if a manager must provide approval when a developer requests vCloud resources, a blocking task might be created. When a developer deploys a vApp, the manager is notified and must approve before proceeding with deployment.

In notifications, also called non-blocking events, a message is sent to the event’s Advanced Message Queuing Protocol (AMQP) broker.