An Empirical Study on API Usages

Abstract

API libraries provide thousands of APIs, and are essential in daily programming tasks. To understand their usages, it has long been a hot research topic to mine specifications that formally define legal usages for APIs. Furthermore, researchers are working on many other research topics on APIs. Although the research on APIs is intensively studied, many fundamental questions on APIs are still open. For example, the answers to open questions, such as which format can naturally define API usages and in which case, are still largely unknown. We notice that many such open questions are not concerned with concrete usages of specific APIs, but usages that describe how to use different types of APIs. To explore these questions, in this paper, we conduct an empirical study on API usages, with an emphasis on how different types of APIs are used. Our empirical results lead to nine findings on API usages. For example, we find that single-type usages are mostly strict orders, but multi-type usages are more complicated since they include both strict orders and partial orders. Based on these findings, for the research on APIs, we provide our suggestions on the four key aspects such as the challenges, the importance of different API elements, usage patterns, and pitfalls in designing evaluations. Furthermore, we interpret our findings, and present our insights on data sources, extraction techniques, mining techniques, and formats of specifications for the research of mining specifications.