Databases Reference
In-Depth Information
E1
E2
E1
Fleaf
=
ALLSup
0,16
E3
=
=
3
E2
E3
E4
E5
E6
Fleaf
=
ALLSup
0,83
IS_ARel
0,11
E4
=
=
1
IS_ARel
0
E5
E6
(a)
(b)
E1
E1
Fleaf
=
ALLSup
0,15
Fleaf
=
ALLSup
0,28
E2
E3
E2
E3
=
=
1,6
=
=
2,2
IS_ARel
0,19
IS_ARel
0,28
E4
E5
E6
E4
E5
E6
(c)
(d)
Figure 14.4
Examples of IS_A relationships.
nonroot entity, ALLSup (the root entity is not counted because it
cannot have parents).
The IS_ARel metric is calculated using the following formula:
Fleaf
ALLSup
IS
_
A
Re
l
=
Fleaf
-
This metric assesses the complexity of each IS_A hierarchy. The
overall IS_ARel
complexity
is
the average
of
all the
IS_ARel
complexities in the E/R model.
Table 14.2 summarizes the meaning of the values of the proposed
closed-ended metrics. Columns indicate the interpretation of measurements
at the extremes of that range and in the middle.
Now we will apply the outlined metrics to the example shown in
Figure 14.5, taken from [43].
Table 14.3 summarizes the values of the metrics calculated for the
example in Figure 14.5.
