Information Technology Reference
In-Depth Information
However
Nr
+
(
mars
.
fits
)
Nr
∗
(
⊂
T
(
u
2
))
.
Disjunctive Dependencies
The previous approach will give incorrect results if we have disjunctive dependen-
cies. For example, consider the dependencies shown in Fig.
8.6
and suppose that all
of them are disjunctive. This means that
o
depends on either
t
1
,or
t
2
. In this case we
have two possible sets for
Nr
+
(o)
;
Nr
+
(o)
{t
1
,t
3
}
and
Nr
+
(o)
{t
2
,t
4
}
.
For capturing disjunctive dependencies we use the rule-based framework
described at Sect.
8.2.1.1
. Figure
8.7
shows the logical architecture of a system
=
=
Fig. 8.6
The disjunctive
dependencies of a digital
object o
Fig. 8.7
A partitioning of facts and rules
