The mapper variable contains all the information of the model considered in a structure of the entity collections are grouped by package / namespace.
Entities can be linked according to two kinds of parent-child relationships:
1. "Children" entities are derived from a base entity, which may or may not be an abstract class.
2. "Related" entities have attributes whose type is defined by another entity.
The two entities at the ends of an Association are each linked to a role.
An association class is encoded as an Entity whose Association is marked by the "isLink" property.