The idea is simple: from one application, capture information from Subversion log, store it in a local SQLite database, then use another application to generate the graphs by optionally using a passed in template. Simple and good design, and it does what you expect, in a something optimized processing (due to database caching technique).
Congratulations to you all svnplot developers and contributors!!!
But, if you like to read source code, probably this is not the right place to look for; if you are looking projects to mastering refactoring techniques, maybe this could be a good start.