Fujitsu UDS/SQL V2.5 사용자 설명서
General information
Relative merits of the data models
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2.2.3
Relative merits of the data models
Comparing the data models with one another in terms of quality is difficult and possible only
from the perspective of a specific field of application. Especially an attempt to weight the
relative advantages and disadvantages of the models can be made only for a specific appli-
cation.
from the perspective of a specific field of application. Especially an attempt to weight the
relative advantages and disadvantages of the models can be made only for a specific appli-
cation.
Basically, all data structures can be implemented with either of the two models.
Advantages of the relational model
The clear advantage of the relational model is its greater flexibility in regard to data struc-
tures.
tures.
Since the application programs are not dependent on the data structures, the data struc-
tures can in many cases be changed without affecting the applications. Through the use of
views, the underlying data structures can be hidden completely from the users.
tures can in many cases be changed without affecting the applications. Through the use of
views, the underlying data structures can be hidden completely from the users.
Advantages of the CODASYL model
A major advantage of the CODASYL model lies in the performance of the application.
The CODASYL model explicitly defines not only the record types and tables, but also their
relationships to one another. This means that the relationships between the record types
must also be known to the applications. Since the applications build on the defined data
structures, the applications are optimally adjusted to them. This adaptation of the applica-
tions to the data structures known to the database system has a very favorable effect on the
applications’ performance.
Of course, this favorable influence of the data structures on the applications is achieved at
the cost of flexibility. In many cases, alterations to the data structures have an effect on the
applications.
relationships to one another. This means that the relationships between the record types
must also be known to the applications. Since the applications build on the defined data
structures, the applications are optimally adjusted to them. This adaptation of the applica-
tions to the data structures known to the database system has a very favorable effect on the
applications’ performance.
Of course, this favorable influence of the data structures on the applications is achieved at
the cost of flexibility. In many cases, alterations to the data structures have an effect on the
applications.
A further advantage of the CODASYL model lies in its monitoring of referential integrity.
A database system based on the CODASYL model automatically ensures that the defined
logical relationships between the record types are not violated.
logical relationships between the record types are not violated.