SMILE v5.1: The Universal Methodology That Turns Any Project Into a Continuously Learning Digital Twin

SMILE (Sustainable Methodology for Interoperable Lifecycle Enablement) is a design-science methodology for building digital twins that continuously learn. This version corrects two definitional errors: the NUDEDA infrastructure-maturity ladder is restored to its correct basis — Weill and Broadbent's (1998) four postures None, Utility, Dependent, Enabler, extended by the author for the age of AI with Digital DNA and Autonomous — and SPIN is used strictly in Rackham's (1988) sense (Situation, Problem, Implication, Need) as the phase-entry questioning logic, with the earlier spatial framework renamed Spatial Twinning (Space, Place, Interaction, Network). The paper presents six phases, four perspectives (People, Systems, Planet, AI), the AEST temporal model, the Crucible trust layer, and a maturity model, positioned as a design-science artefact (Hevner et al., 2004) and working-paper corpus anchor under CC-BY-4.0.