expiresAt
A similar special property for entities exists in NGSIv2. The idea is that at the time identified by expiresAt, the Entity is deleted. Such an entity is referred to as a transient Entity.
While this can easily be implemented in a centralized setting, there are lots of issues in a distributed setting.
- expiresAt may be set for the Entity in one Broker, but not the other
- one Broker is not aware, on which other Broker an Entity is stored
- it is only partially deleted, even though the user expects complete deletion
- clock synchronization is an issue, because out-of-sync clocks result in an Entity being deleted earlier or later
Solution may be not to say, the entity or attribute as such is transient, but the local storage of it - so expiresAt only ever applies where it is set - it never applies to information about the same entity stored elsewhere, where expiresAt is not set.