Guard: A relative debugger

A significant amount of software development is evolutionary, involving the modification of already existing programs. To a large extent, the modified programs produce the same results as the original program. This similarity between the original program and the development program is utilized by relative debugging. Relative debugging is a new concept that enables the user to compare the execution of two programs by specifying the expected correspondences between their states. A relative debugger concurrently executes the programs, verifies the correspondences, and reports any differences found. We describe our novel debugger called Guard, and its relative debugging capabilities. Guard is implemented by using our library of debugging routines, called Dynascope, which provides debugging primitives in heterogeneous networked environments. To demonstrate the capacity of Guard for debugging in heterogeneous environments, we describe an experiment in which the execution of two programs is compared across Internet. The programs are written in different programming languages and executing on different computing platforms