Create a description of a system

From time to time, I must provide a scheme on how a system works. It is not really to find a technique in which all details can be shown. I was to make a differentiation between processes, like sending mail, databases and applications. I also want to indicate what techniques are used. Moreover, I would like to indicate which elements belong to each other. I then misuse the SDL stencil in Visio. This allows to make such distinction. See the figure below:
. There within the arrows, the techniques can be shown. I also use the separated processes to indicate which applications are used with the platform on which they run. Finally this stencil has a diagramme for databases which is most convenient. Another example can be found here