Analyzing the Evolution of the Source Code Vocabulary

Source code is a mixed software artifact, containing information for both the compiler and the developers. While programming language grammar dictates how the source code is written, developers have a lot of freedom in writing identifiers and comments. These are intentional in nature and become means of communication between developers. The goal of this paper is to analyze how the source code vocabulary changes during evolution, through an exploratory study of two software systems. Specifically, we collected data to answer a set of questions about the vocabulary evolution, such as: How does the size of the source code vocabulary evolve over time? What do most frequent terms refer to? Are new identifiers introducing new terms? Are there terms shared between different types of identifiers and comments? Are new and deleted terms in a type of identifiers mirrored in other types of identifiers or in comments?