These subjects are dealt with here:
General information on attributes
Attributes that describe the entities of an entity type are normally assigned to an entity type. In other words, the attributes of an entity type determine the properties it can have.
Attributes are either assigned directly to an entity type, taken over from the ABAP/4 Dictionary or inherited from a generalization.
Attributes that were transferred to the entity type when a table or view was assigned are indicated by an entry in the column Dic. Attributes that the entity type inherited from the generalization are indicated by an entry in the column Inh.