Abstract
Developers need software models to make decisions while developing software systems. Static software models are commonly imported by parsing source code. But building a custom parser is a difficult task in most programming languages. To build such a custom parser the grammar of the programming language is needed. If the grammar is not available, which is the case for many languages and notably dialects, it has to be inferred from the source code. Automatically finding the keywords of those languages can help the process of inferring a grammar because many keywords identify beginnings and endings of the basic building blocks of programs. We tested four heuristics of finding keywords in source code of unknown languages: i) the most common words are keywords; ii) words that occur in most of the files are keywords; iii) words at the first position of the line before an indent are keywords; and iv) words at the beginning of a line are keywords. With our third method we achieved the best results. It found 26 of the 50 Java keywords, 10 out of 17 of the Shell keywords and 9 out of 20 of the Haskell keywords. Our data suggests that the more source code is available the more precise the results get. Adding more source code produced the most improvements when using the first or second method.