Plasma fluid models like B2, UEDGE or EDGE2D are the standard tools for simulation of scrape-off layer physics, both for design and experimental support. The concept of a numerical tokamak, aiming at a predictive code for ITER, triggers the need to re-assess the available tools and their necessary extensions. These additional physics issues will be summarized. The experience existing in other scientific fields with multi-scale problems and modelling should be used as a guide. Here, the coupling strategies are in particular of interest for fusion problems. As a consequence, a certain construction of integrated modelling codes is needed: depending on the specific problem, models allowing different levels of complexity will be needed. Therefore, a hierarchy of tools is necessary, which will be discussed.