A notification is a direct means to communicate information to the user and keep them continuously in touch with the application. It is composed of strata of component, hence of functions; schematically goes from a source, that is the origin of the information in any given App –which varies accordingly with the variation of the App’s architecture.
The message carried is signaled to the receiver through a notification Badge, a visual indicator that drives users to the conveyed message. A badge is not to be confused with the anchor, which is also a visual indicator or the vessel that carries the notification. A notification comes in two types: informative and actionable, differing from one application to another.
A notification may be in several types and shapes: Notification Center (Medium), Source Anchored notification (What’sApp), Mixed Model (Facebook), It is paramount to know when and how to use the adequate type of notification accordingly with the type/function of the information!
Source: https://medium.muz.li/designing-notifications-for-applications-3cad56fecf96