- User Description (UD): a set of descriptions which may contain static and dynamic information about the user, including some other data like the history of the user's interactions, preferences, security settings regarding these information, etc.

- Context Description (CD): a set of descriptions of the environmental situation in which the user operates, e.g., user's device in use, physical position, environmental variables (temperature, humidity, sound level, etc.), security settings regarding these inform ation, etc.

- Service Description (SD): a set of descriptions containing information (including security settings) about the service (or a set of sub-services), that is offered to the end-user application, e.g. video on demand, maps, etc.

- Recommendation Description (RD): a set of descriptions containing information about recommended items, provided when a customer requests a service in a certain context and in a certain environment. RD may include 1) the recommended content, 2) information extracted from UD, CD, SD, 3) additional logical relations among UD/CD/SD (or their subsets) and 4) metadata from UD/CD/SD.

ISO/IEC 21000-22:2016 specifies User Description, Context Description, Service Description and Recommendation Description. Description Managers, Recommendation Engine and Application are outside of the scope of this document.