Database Reference
In-Depth Information
AcctNo
OverdraftAmt
CHECKING
ACCOUNT
DateOfBirth
ISA
NumOfChecks
STANDARD
PREMIUM
GOLD
MinPymnt
InterestPymnt
CHECKINGACCOUNT (
AcctNo
, OverdraftAmt)
STANDARD (
AcctNo
, OverdraftAmt, NumOfChecks)
Foreign Key:
AcctNo
REFERENCES
CHECKINGACCOUNT
Relationa
l
Notation
PREMIUM (
AcctNo
, OverdraftAmt, InterestPymnt, MinPymnt)
Foreign Key:
AcctNo
REFERENCES
CHECKINGACCOUNT
GOLD (
AcctNo
, OverdraftAmt, DateOfBirth)
Foreign Key:
AcctNo
REFERENCES
CHECKINGACCOUNT
Figure 9-21
Transformation of superset and subsets.
Comparison of Models
By now, you have a fairly good grasp of the principles of transformation of a seman-
tic data model into a relational data model. We took each component of the seman-
tic data model and reviewed how the component is transformed into a component
in the relational model. Let us list the components of the semantic data model and
note how each component gets transformed. Although most of our discussion so far
in this chapter has used the semantic model with the object-based modeling tech-
nique, we list the components of the entity-relationship data model here. This will
further confirm that whether your semantic data model is arrived at through object-
based data modeling or entity-relationship data modeling, the transformation
process is the same.
The components of the semantic data model and how they are transformed into
relational data model follow:
Entity Type
Strong
Transform into relation.
Weak
Transform into relation. Include the primary key of the identifying
relation in the primary key of the relation representing the weak entity type.
Attribute
Transform attribute name into column name.
Translate attribute domains into domains for corresponding columns.
Simple, single-valued
Transform into a column of the corresponding relation.
Composite
Transform into columns of the corresponding relation with as many
columns as the number of component attributes.
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