Page 85 - SOFTWARE TESTING & QUALITY ASSURANCE

Software Testing and Quality Assurance

We will now analyze backward and forward compatibility through a simple example:

Figure 6.1: Backward and Forward Compatibility

The simplest example for backward and forward compatibility is the .txt or text file. Figure 6.1 shows a
text file created using Notepad 98 that runs under Windows 98 (it is backward compatible) and can be
tested all the way back to MS-DOS 1.0. It is also forward compatible to Windows XP Service Pack 2 and
is expected to go beyond that as well.
It is not necessary for all files and software to be backward and forward compatible. Software designers
make decisions related to testing requirements for forward and backward compatibility of the software.
Backward compatibility is similar to the concept of using old programs once again with new standards.

Forward compatibility is the compatibility checking of a product with the future versions of the
software. For example, the new changes that have been considered for the next FORTRAN version are
improved with parallel treatments like interrupt handling, parameterized data types, and inherited data
types.

1. When the migration occurred from Fortran 66 to Fortran 77, the extended
DO-loop was removed considering the fact that the extended DO-loop
means that if you do not change any of the DO-loop parameters you can
jump out of the loop and then jump in again. This is similar to the
concept of structured programming.

2. The Hollerith constants were removed (except in FORMAT).

The above example implies that some programs that work with Fortran 66 do not work with Fortran 77.
Hence, manufacturers have included these two concepts in their FORTRAN implementations.
The incompatibility between Fortran 66 and Fortran 77 is related to the assumed size allocation of
dummy arrays.

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