Subroutine libraries

are the oldest and the most successful reuse technique and have been applied to package reusable code in areas as disparate as operating system services, input/output routines, mathematical functions, graphics, databases, multi-media, and more. Each library provides a language-specific (e.g., Fortran, C, COBOL) interface, but the same library may be accessible from different languages. A typical example is a library of mathematical functions that can be called from both Fortran and C. The data exchanged between the subroutines in the library and the program using the library are restricted to data types of the host language. However, when subroutine libraries mature, their size tends to grow geometrically. This is due to all the feature variations that have to be provided regarding, for instance, precision, robustness, algorithm used, efficiency, and memory usage. This calls for sophisticated search and retrieval methods such as, for instance, described by Prieto-Diaz & Freeman (1987).