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However, in disjoint generalization, there are no duplicate element instances in two
different element type instances under the same parent element instance. On the
other hand, there is no such restriction in overlap generalization (Fig.
4.21
).
Case 2: Overlap Generalization
(Fig.
4.22
)
Rule 7: Mapping Categorization from RDB to XML
In converting categorization relational tuples into XML instances, we must ensure
that each child tuple is converted into only one child element instance under a par-
ent element instance (Fig.
4.23
).
Rule 8: Mapping n-ary Relationship from RDB to XML
In converting n-ary relational tuples into XML instances, we must ensure that the
parent relations are converted into component element instances under a group ele-
ment in an XML document (Fig.
4.24
).
RelationA
A1
a11
a12
XMLDocument
A2
a21
a22
<A A1="a11" A2="a21">
<B B1="b11"></B>
</A>
Data
RelationB
*A1
a11
B1
b11
Conversion
<A A1="a12" A2="a22">
<C C1="c11"></C>
</A>
Relation C
*
A1
a12
C1
c11
Fig. 4.21
Disjoint generalization: data conversion
Relation A
A1
a11
a12
A2
a21
a22
XMLDocument
<A A1="a11" A2="a21">
<B B1="b11"></B>
<C C1="c11"></B>
</A>
Relation B
*
A1
a11
Data
B1
b11
Conversion
<A A1="a12" A2="a22">
<C C1="c12"></C>
</A>
Relation C
*
A1
a11
C1
c11
a12
c12
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