For various reasons, such as new requirements, architecture refactoring, and bug fixing, software projects often evolve to yield better quality and performance. All changes produced during the development process are reflected in the source code, which provides an opportunity to explore software evolution. In this paper, we propose a visual analytics system to support evolution analysis based on topic modeling. We focus on three aspects: (1) when significant changes to source code occur, (2) how software features evolve, and (3) why software evolution occurs. Each source file is regarded as a document and represented by its topic vector. The files of each two successive versions are classified into four types to quantify version differences, and the number of topic-associated files is denoted as the topic assignment to characterize feature evolution. Finally, we inspect the causes of software evolution through the visual comparison between versions. Two case studies on JavaScript libraries demonstrate the usefulness and effectiveness of our system.

由于各种原因，例如新要求，体系结构重构和错误修复，软件项目通常会不断发展以产生更好的质量和性能。在开发过程中产生的所有更改都反映在源代码中，这提供了探索软件演化的机会。在本文中，我们提出了一种可视化分析系统，以支持基于主题建模的演化分析。我们专注于三个方面：（1）当源代码显著发生变化;（2）如何软件功能演变，以及（3）为什么发生软件演变。每个源文件都被视为文档，并由其主题向量表示。每个两个连续版本的文件分为四种类型，以量化版本差异，并将与主题相关的文件的数量表示为主题分配，以表征特征演变。最后，我们通过版本之间的直观比较来检查软件演进的原因。关于JavaScript库的两个案例研究证明了我们系统的有用性和有效性。