I”m having to work with legacy code (mostly CFML) with very little or no documentation, no domain model of any sort to follow either.
To start building some sense out of it, I though ‘start keeping notes’, then wondered if plain old journal and pencil for text notes would do. Maybe a text document (searchable). Or is it best to take the plunge and UML the beast over time? If that’s an overkill on one hand, on the other I repeatedly find myself feeling around the elephant over and over again. How do you build a up a map of the territory?
Sorry for the late answer, but I’ve ended in situations like this couple of times before. I’d suggest you not to create UML for that, since it will take much time and this code is not very nice, as you’ve noted (no domain model, no structure).
You could use pen and paper, or text file. Browse through the code, find the most important parts for you and write down where it is located, with some description. If there is no data structure, you could use file name, module, line number, etc. After spending some time doing this, you will have something like navigation plan for the part of the system and general understanding of how it works.
Also, you should refer to this question, there are some answers that can be useful.