iX V6.5 (30391-90011)

Chapter 1 29

Introduction

Program Maintenance

Throughout the life of a system, processing requirements evolve as the usefulness of the

data is explored. As ﬁle organization concepts change with the needs of the application,

some data restructuring can be done with little impact on existing programs. Changes to

the structure of an existing database affect only those programs that process the changed

data; no other programs in the system need to be recompiled to reﬂect the new database

structure.

The evolution of the database is not limited by the need to balance the cost of changing an

existing system against the beneﬁts to be derived from the new structure. It is not

necessary to do a "where-used" evaluation on a data item carried in multiple ﬁles to assess

the impact of a data change on existing systems.

Finally, the accessibility of data is not limited by design decisions made during initial

system design. The structure of a database can evolve with the needs of the application

user. The application designer no longer has to anticipate the needs of the user across the

full life of the system.

Program File Independence

Conventional ﬁle structures tend to be rigid and inﬂexible. The nature of conventional ﬁle

management systems requires that the logic of application programs be intricately

interwoven with ﬁle design. When it is necessary to alter the structure of a ﬁle, a program

must be written to change the ﬁle and programs that access the ﬁle must be changed to

reﬂect the ﬁle change. Because change is the rule rather than the exception in data

processing, a large percentage of total time and manpower is spent reprogramming.

TurboIMAGE/XL allows the data structure to be independent of the application program.

Data item relationships are independently deﬁned. Changes in the database structure

need only be incorporated into those programs that manipulate the changed data. User

programs need to view only that portion of the database description that pertains to each

program's processing requirements. Because all references to the database are resolved at

execution time, only those programs affected by changes to the database description need

to be changed.