Data Conversion - Information Systems Reengineering, Integration and Normalization - page 171

Rule 4: Mapping Aggregation from RDB to XML
In converting aggregation relational tuples into XML instances, we must ensure
the component relational tuples are converted into the component elements under a
group element in an XML document (Fig. 4.19 ).

Rule 5: Mapping ISA relationship from RDB to XML
In converting isa relational tuples into XML instances, we must ensure that the
subclass relational tuples are converted into child element instances without the
duplication of superclass relational key (Fig. 4.20 ).

Rule 6: Mapping Generalization from RDB to XML
Case 1: Disjoint Generalization
Similar to an isa relationship, in converting generalization relational tuples into
XML instances, we must ensure that the subclass relational tuples are converted
into child element instances without the duplication of superclass relational key.

Relation A
A1
a11
a12

A2
a21
a22

XMLDocument

<A A1="a11" A2="a21">
<Group>
<B B1="b11" B2="b21" B_id="1"></B>
<R1 B_idref="1" C_idref="2"></R1>
<C C1="c11" C2="c21" C_id="2"></C>
</Group>
</A>

Relation B
B1
b11

B2
b21

b12 b22 Data

Relation C
C1
c11

Conversion

C2
c21

<A A1="a12" A2="a22">
<Group>
<B B1="b12" B2="b22" B_id="3"></B>
<R1 B_idref="3" C_idref="4"></R1>
<C C1="c12" C2="c22" C_id="4"></C>
</Group>
</A>

c12 c22

Relation R1

* B1
b11

* C1
c11

*A1
a11

b12 c12 a12

Fig. 4.19 Aggregation: data conversion

Relation A
A1
a11
a12

XMLDocument

A2
a21
a22

<A A1="a11" A2="a21">
<B B1="b11" ></B>
</A>

Data

Relation B
* A1
a11

Conversion

B1
b11

<A A1="a12" A2="a22"></A>