||Base class for all data objects, which want to track when they were created
and which belongs to some partition (called domain).
||Definition of common data constants.
||Base class for all data objects regardless of how they are persisted.
||Base class for all data objects, which can be modified and therefore want to
track when they were last modified.
||This class is the simplest case of modifiable data object and it is useful in
situations when we need transfer only the most basic identification information
skipping the business data.