Thanks for all your advice, I summed it up and this is what my proposal for the SoC-application will look like (Yes, I know I have to submit it to Google): (1) Classes for SVG primitives. This includes paths, circles, ellipses, rectangles, polygons, lines and polylines. Styles for strokes and fills end up in a base class. (2) "Draw"-mechanism. Primitives are hold in a layer's container from where their "to_svg()"-methods are called and the strings are put together based on their position inside the layer and the layer's position. (3) Graph plotter. Provides functions for plotting graphs from container-data. Includes options for color and shape (dots, linear connections, quadratic connections, columns, ...), just as options for the co-system (grid?, height, length, ...) and a positionable legend. Nothing spectacular, everything was said before, however, comments again appreciated. Thanks, Johannes