A great deal of work on software maintenance focuses on source code analysis and manipulation. Code is viewed as a static entity that is -more or less -separated from the system at runtime. Although there are certainly important open questions in this field, the separation of code and runtime imposes itself an obstacle for the evolution of continuously functioning systems. The goal of the work presented in this paper is to blur the separation between statics and dynamics of a software system on

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... a conceptual level. To achieve this, we propose a system model that combines space, time and level of abstraction and a conceptual framework for incremental evolution of systems during execution. Based on this continuously functioning systems can be maintained in a highly flexible and conceptually sound way.