Data Conversion - Information Systems Reengineering, Integration and Normalization - page 169

standalone (nonparticipating) child relation tuples, they can only be converted into
child element instances under an empty parent element instance.

Case 1: Total/Mandatory Participation (Fig. 4.14 )

RelationA
A1
a11
a12

XMLDocument

A2
a21
a22

<A A1="a11" A2="a21">
<B B1="b11" B2="b21"></B>
</A>

Data

Relation B
B1
b11

Conversion

<A A1="a12" A2="a22">
<B B1="b12" B2="b22"></B>
<B B1="b13" B2="b23"></B>
</A>

B2
b21

*A1
a11

b12 b22 a12

b13 b23 a12

Fig. 4.14 Total participation: data conversion

Case 2: Partial/Optional Participation (Fig. 4.15 )

Relation A
A1
a11
a12

A2
a21
a22

XMLDocument

Data

<A A1="a11" A2="a21">
<B B1="b11" B2="b21"></B>
</A>

Relation B
B1
b11

Conversion

B2
b21

*A1
a11

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

b12 b22 null

<A></A>
<B B1=“b12” B2=“b22”></B>

Fig. 4.15 Partial participation: data conversion

Rule 3: Mapping Cardinality from RDB to XML
In converting one-to-one relational tuples into XML instances, we must ensure
that each parent element instance consists of one child element instance only. In
converting one-to-many relational tuples into XML instances, each parent element
instance can have multiple child element instances. In converting many-to-many
relational tuples into XML instances, a pair of ID and IDREF in two element types
are applied such that they refer to each other in many-to-many associations.