1.   The particular attribute or group of attributes that uniquely identifies an entity occurrence is known as the key attribute or attributes.

2.   An entity occurrence is a particular example of an entity which can be uniquely identified.

3.   The values of a set of attributes will distinguish one entity occurrence from another.

4.   For an EMPLOYEE entity, for example, an EMPLOYEE entity occurrence who happens to be a manager manages other occurrences of the entity EMPLOYEE.

5.   The key attributes will uniquely identify any entity occurrence.

6.   Each entity must be normalised to third normal form once the entity occurrences have been added to the model.

7.   In hierarchical model, each node represents a record type and each entity occurrence of a record.

8.   In this approach, as with hierarchies but unlike the relational model, there are explicit links between related entity occurrences.