On the implementation and correctness of information system upgrades

Information systems are applications incorporating a database for storing and processing data. Upgrading information systems requires updating the application logic, modifying the database schema, and adopting the data accordingly. Previous research focuses either on schema evolution or on application logic updates. In this paper, we take a holistic approach by addressing the combination. First, we elaborate the three main upgrade patterns: install & copy, rejuvenation/delta only, and rejuvenation/verified. Second, we introduce our upgrade correctness concept. It is a formal correctness criterion for deciding whether an upgrade succeeded. Third, we discuss implementation patterns. Our insights base on various upgrade projects from stand-alone applications to multi-tenant systems having affected more than one hundred banks.