ECS 165B Database Systems
Extended Entity-Relationship Model (EER Model)
The objective of the EER model is to make some object-oriented aspects more explicit, in particular the modeling
of (complex) attributes associated with entity types.
Object-valued attribute:
The first diagram shows an object-valued attribute
associated with the entity type E1. Each entity of type E1
has exactly one attribute of type E2 (in addition to p
some other attributes). An entity of type E2 must always
be associated with at least one entity of type E1 (existen
dependency).
E1 E2
A:
E1 E2
A
(0,1)
erhaps
ce
In the “plain” ER model, this aspect would be modeled as
shown in the second diagram.
Complex-valued attributes:
There are several types of complex-valued attributes that can be associated with an entity type.
Set-valued attribute:
Here, an entity of type E1 has a set of entities of type E2 a
single attribute. For example, a person has a set of
addresses; each address would be an entity on its own. As
above, the existence of an entity of type E2 depends on
whether it is part of an attribute value of an entity of type
E1.
E1 E2
A:
set
of
E1 E2
A
(0,*)
s
The same can be modeled in the plain ER model, as shown
on the right.
List-valued attribute:
Here, an entity of type E1 has a list of entities of type E2 a
single attribute. For example, a book has a list of aut
each author would be an entity on its own. As above, th
existence of an entity of type E2 depends on whether it i
part of an attribute value of an entity of type E1.
s
hors;
e
s
gain, the same can be modeled in the ER model as shown
he case for a bag-valued attribute would be the same,
ote about Cardinality Constraints: With a complex- ,
st
E1 E2
A:
list
of
E1 E2
A
(0,*)
position
A
on the right.
T
except that in the plain ER model, one would name the relationship type attribute “occurrences”.
N
valued attribute, cardinality constraints can be associated
specifying how many members there have to be in the set,
list, of bag. For example, the following notation would
specify that the list-valued attribute named A associated
with an entity of type E1has at least 2 members and at mo
8 members (min at the bottom, max at the top).
E1 E2
A:
list
of
2
8
Dr. Michael Gertz
