Vocabulary Normalization Improves IR-Based Concept Location

Tool support is crucial to modern software development, evolution, and maintenance. Early tools reused the static analysis performed by the compiler. These were followed by dynamic analysis tools and more recently tools that exploit natural language. This later class has the advantage that it can incorporate not only the code, but artifacts from all phases of software construction and its subsequent evolution. Unfortunately, the natural language found in source code often uses a vocabulary different from that used in other software artifacts and thus increases the vocabulary mismatch problem. This problem exists because many natural-language tools imported from Information Retrieval (IR) and Natural Language Processing (NLP) implicitly assume the use of a single natural language vocabulary. Vocabulary normalization, which goes well beyond simple identifier splitting, brings the vocabulary of the source into line with other artifacts. Consequently, it is expected to improve the performance of existing and future IR and NLP based tools. As a case study, an experiment with an LSI-based feature locator is replicated. Normalization universally improves performance. For the tersest queries, this improvement is over 180% (p < 0.0001).