A Formal Study on Backward Compatible Dynamic Software Updates

TL;DR

This paper provides a formal framework for backward compatible dynamic software updates, ensuring that updated programs interact correctly with unchanged environments, and introduces classes of such updates based on a novel program equivalence framework.

Contribution

It introduces a formal definition of backward compatibility for dynamic updates and classifies update types using a new program equivalence framework applicable to non-terminating executions.

Findings

Backward compatible updates constitute about 32% of real-world program changes.

Proposes a typed extension of W language for formal analysis.

Defines classes of updates based on a generalized program equivalence.

Abstract

We study the dynamic software update problem for programs interacting with an environment that is not necessarily updated. We argue that such updates should be backward compatible. We propose a general definition of backward compatibility and cases of backward compatible program update. Based on our detailed study of real world program evolution, we propose classes of backward compatible update for interactive programs, which are included at an average of 32% of all studied program changes. The definitions of update classes are parameterized by our novel framework of program equivalence, which generalizes existing results on program equivalence to non-terminating executions. Our study of backward compatible updates is based on a typed extension of W language.