Recent work has shown that although programming languages en- able source code to be rich and complex, most code tends to be repetitive and predictable. The use of natural language processing (NLP) techniques applied to source code such as n-gram language models show great promise in areas such as code completion, aiding impaired developers, and code search. In this paper, we address three questions related to different methods of constructing lan- guage models in an industrial context. Specifically, we ask: (1) Do application specific, but smaller language models perform better than language models across applications? (2) Are developer specific language models effective and do they differ depending on what parts of the codebase a developer is working in? (3) Finally, do language models change over time, i.e., does a language model from early development model change later on in development? The answers to these questions enable techniques that make use of programming language models in development to choose the model training corpus more effectively.
We evaluate these questions by building 28 language models across developers, time periods, and applications within Microsoft Office and present the results in this paper. We find that developer and application specific language models perform better than models from the entire codebase, but that temporality has little to no effect on language model performance.