Information Technology Reference
In-Depth Information
m
A
b
n
E
a
R
1
E
b1
E
b2
E
a
E
a
E
a
A2
A1
A1
R
b
A1
A1
E
x
1
R
1
R
1
1
isa
n
isa
n
n
R
A
A
c
A
b
E
b
E
b
A2
E
b
A2
A2
n
E
b
n
E
a
A3
a) Cardinality
d) Participation
b) Weak Entity
c) isarelationship
a) Cardinality
c) isarelationship
e) aggregation
A
c
A
c
M
E
x
A
c
A
c
E
x1
E
x2
M
E
a
M
M
A
d
A
e
A
d
d=disjoint generalization
o=overlap generalization
:
:
:
d/o
:
C
R
N
A
c
A
d
A
c
A
e
E
a
E
b
N
N
A
c
A
c
N
E
a
E
b
E
c
A
c
M:
N
A
c
M:
N
f) Generalization
g) Categorization
h) N-aryrelationship
Fig. 2.5
Eight data semantics in extended entity relationship model (EER)
ization in which subclass entities can overlap each other and can be differenti-
ated by fields in the superclass entity.
• Categorization—Morethanoneisarelationshipformdataabstractionamongen-
tities such that the union of entities form a superclass entity to a subclass entity.
• Aggregation—Therelationshipbetweenentitiesandrelationshipscanbeaggre-
gated (grouped) as an entity.
In summary, an EER model consists of eight data semantics as shown in Fig.
2.5
(Teorey et al.
1986
).
Figure
2.5
illustrates different data semantics including:
a. One-to-many cardinality between entities E
a
and E
b
b. Weak entity E
b
concatenates the key of A1 from E
a
c. Subclass entity E
b
is a subset of entity E
a
with the same key A
b
A
c
d. Entity E
b
is in total participation with Entity E
a
e. Binary relationship R
b
of entity E
b1
relating with entity E
b2
is an aggregate entity
f. Subclass entity E
a
and E
b
can be generalized into superclass entity E
x
g. Subclass E
a
is a subset of the union of superclass entity E
x1
and E
x2
h. Entities E
a
, E
b
, and E
c
are in many-to-many ternary relationship
A sample of an EER model for a hospital patient record system is in Fig.
2.6
. A
patient is insured by many insurance coverage. A patient belongs to many record
folders. Each record folder contains many medical records. An AE record, a ward
record, and an outpatient record can be generalized as medical record.
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