Information Systems Reengineering, Integration and Normalization - Information Systems Reengineering, Integration and Normalization - page 13

safe approach permitting the old system to return to operation when problems
crop up in the new system. However, handling two systems at the same time
requires extra effort.
• DirectCut-Over:Thisapproachconvertsapplicationprogramsandotherdatato
replace the old one in a specified period of time. It is less costly than the parallel
approach and is well-suited to conversion projects involving a small system.
• Phase-In:Thisapproachisemployedwhenthesystemisverylargeandcannot
be completely converted in one go. It divides the whole conversion process into
several phases.
To successfully convert an information system, people such as software engineers,
users, managers, and operations personnel must have a common ground to discuss
with one another their individual needs, goals, expectations, and constraints, and the
goals of the organization. A common ground can be established by holding regular
meetings for the related parties. The result of the meetings should be management
commitment, transportable documentation that is understandable by appropriate
parties, and a jointly owned, user-oriented set of structured models of the systems
design. These models should contain why, what, where, and how the conversion
will affect the organization. In brief, users' involvement is an essential factor in all
phases of the conversion: planning, requirement, design, construction, implementa-
tion, and operation.
On the technical side, system conversion can be separated into two main parts:
program conversion and data conversion. Converting programs will be less prob-
lematic if the installation has good software quality standards. Problems arise when
such quality standards do not exist or when they are loosely enforced.
Many software vendors supply software utility tools to help clients convert their
databases. For example, Computer Associates International Ltd. has a software tool
called ESCAPE DL/1, which translates the input-output statements in IMS to that
in IDMS so that IMS programs can access IDMS databases without converting the
data. (IMS and IDMS are DBMS supplied by IBM Corp.) Computer Associates In-
ternational Ltd. also supplies programs to convert specification blocks in IMS into
corresponding IDMS schemas and subschemas, including those that help unload
IMS databases to sequential files and reload them into IDMS databases. Figure 1.4
describes the function of ESCAPE DL/1 (CA, 1992 ).
Data conversion can be very complicated if the existing data organization is very
different from the new database model. Similar to program conversion, some soft-
ware vendors also provide utilities for data conversion. One example is converting
sequential files to a database system called ADABAS.
The use of customer-made programs is the more common approach to converting
existing files, but this has several serious shortcomings. Each translation required is
handled by a specially written program that is used only once, hence, a costly solu-
tion. Such programs may be unreliable for restructuring complex databases because
of possible program error or data misinterpretation. This process becomes even
more complex if the conversions of software and hardware are going on at the same
time. Although the use of the generalized program can overcome such problems,