Abstract. We report the use of MGS, a declarative and rule-based language, for the modeling of various self-assembly processes. The approach is illustrated on the fabrication of a fractal pattern, a Sierpinsky triangle, using two approaches: by accretive growth and by carving. The notion of topological collections available in MGS enables the easy and concise modeling of Wang tiles on various lattice geometries as well as more arbitrary constructions of multi-dimensional objects.