Dynamicity is an important requirement for critical software adaptation where a stop can be dangerous (e.g. for humans or environment) or costly (e.g. power plants or production lines). Adaptation at run-time is also required in context-aware applications where execution conditions often change. In this paper, we introduce MaD- cAr, an abstract model of dynamic automatic adaptation engines for (re-)assembling component-based software. MaDcAr aims at being a conceptual framework for developing customizable engines reusable in multiple applications and execution contexts. Besides, MaDcAr provides a uniform solution for automating both the construction of application from scratch and the adaptation of existing component assemblies.