The document discusses three types of relationship degrees: unary, binary, and ternary. Unary relationships involve a single entity, binary relationships involve two entities, and ternary relationships involve three entities. Recursive relationships involve the same entity associated with itself. Examples of recursive relationships given include an employee managing other employees, a course being a prerequisite for other courses, and a part containing other parts.

1. Relationship degree
- Indicates the number of
entities or participants
association with a
relationship.

2. Three types of
Relationship degree
1. Unary relationship
2. Binary relationship
3. Ternary relationship

3. 1. Unary relationship
- Exist when an association is
maintained within a single entity.
“Recursive
Relationship”

4. 2. Binary relationship
- Exist when two entities are
associated in a relationship.

5. 3. Ternary relationship
- Exist when three entities are associated. Although
higher degrees exist, they are rare and are not
specifically named.

6. Three types of relationship degree

7. 1. A DOCTOR writes one or more PRESCRIPTIONs.
2. A PATIENT may receive one or more PRESCRIPTIONs.
3. A DRUG may appear in one or more PRESCRIPTIONs.

8. “Recursive Relationship”
-Is one in which a relationship can
exist between occurrences of the
same entity set.

9. For example:
1:M UR “an EMPLOYEE may manage many EMPLOYEEs,
and each EMPLOYEEs managed by one EMPLOYEE”
1:1 UR “an EMPLOYEE may be married to one and only
one other EMPLOYEE”
M:N UR “ a COURSE may be a prerequisite to many other
COURSEs, and each COURSE may have many other
COURSEs as prerequisites.

10. 1:1 UR “an EMPLOYEE may be married to
one and only one other EMPLOYEE”

11. Unary relationship are common
in manufacturing industries…

12. Implementation of the recursive relationship
“PART contains PART”

13. The M:N recursive relationship might be
more familiar in a school environment…

14. The 1:M recursive relationship
“EMPLOYEE manages EMPLOYEE”

15. Participation as described is bidirectional, meaning
that it must be addressed in both directions along
the relationship.
•Must every employee have a spouse who is
an employee?
•Must every employee be spouse to
another employee?

16. “NO” … it is possible to be an
employee and not have another
employee as a spouse. Also it
possible to be an employee and
not be the spouse of another
employee…

17. Associative (composite) Entities
-In the original ERM described by Chen,
relationships do not contain attributes.
-The associative entity is used to
implement a M:N relationship between
two or more entities.
-Also known as a “Composite or Bridge
entity”

18. Example of Bridge .