In the simple example programs in Chapters 1 and 3, we demonstrated how a mapping file could be used to establish the relationship between the object model and the database schema. A mapping file can map a single class or multiple classes to the database. The mapping can also describe standard queries (in HQL and SQL) and filters.
Although we have referred to the Hibernate types in passing, we have not discussed the terminology in any depth. In order to express the behavior of the mapping file elements, we need to make these fine distinctions explicit.
Hibernate types fall into three broad categories: entities, components, and values.
Generally, an entity is a POJO ...