Schema Translation - Information Systems Reengineering, Integration and Normalization - page 118

Case 1: Disjoint Generalization

EERModel DTDGraph

A1
A2

A1
A2

Entity A Element A

d | Schema

Translation

A1
B1

A1
C1

Entity B EntityC B1 ElementB Element C C1

DTD

Relational Schema

<!ELEMENTA(B |C)>
<!ATTLISTAA1 CDATA#REQUIRED>
<!ATTLISTAA2 CDATA#REQUIRED>
<!ELEMENTBEMPTY>
<!ATTLISTBB1 CDATA#REQUIRED>
<!ELEMENTCEMPTY>
<!ATTLISTCC1 CDATA#REQUIRED>

RelationA( A1 ,A2)
RelationB(* A1 ,B1)
RelationC(* A1 ,C1)

Fig. 3.50 Schema translation of disjoint generalization

Case 2: Overlap Generalization

EERModel DTDGraph

A1
A2

A1
A2

Entity A ElementA

o ? Schema

Translation

A1
B1

A1
C1

B1 C1

EntityB Entity C ElementB ElementC

DTD

Relational Schema

<!ELEMENTA(B?, C?)>
<!ATTLISTAA1 CDATA#REQUIRED>
<!ATTLISTAA2 CDATA#REQUIRED>
<!ELEMENTBEMPTY>
<!ATTLISTBB1 CDATA#REQUIRED>
<!ELEMENTCEMPTY>
<!ATTLISTCC1 CDATA#REQUIRED>

Relation A( A1 ,A2)
Relation B(* A1 ,B1)
Relation C(* A1 ,C1)

Fig. 3.51 Schema translation of overlap generalization

Rule 8: Mapping Categorization from RDB to XML
A subclass table is a subset of a categorization of its superclass tables. In other
words, a subclass table is a subset of a union superclass tables such that the data
occurrence of a subclass table must appear in one and only one superclass table. In
DTD, we transform the super classes into elements, and their common subclass into
an element on the same level. Each element receives an additional “artificial” ID