Web APIs: Features, Issues, and Expectations - A Large-Scale Empirical Study of Web APIs From Two Publicly Accessible Registries Using Stack Overflow and a User Survey

With the increasing adoption of services-oriented computing and cloud computing technologies, web APIs have become the fundamental building blocks for constructing software applications. Web APIs are developed and published on the internet. The functionality of web APIs can be used to facilitate the development of software applications. There are numerous studies on retrieving and recommending candidate web APIs based on user requirements from a large set of web APIs. However, there are very limited studies on the features of web APIs that make them more likely to be used and the issues of using web APIs in practice. Moreover, users' expectations on the development and management of web APIs are rarely investigated. In this paper, we conducta large-scale empirical study of 20,047 web APIs published at two popular and publicly accessible web API registries: ProgrammableWeb and APIs.guru. We first extract the questions posted in Stack Overflow (SO) that are relevant to the web APIs. We then manually analyze 1,885 randomly sampled SO questions and identify 24 web API issue types (e.g., authonzation error) that are encountered by users. Afterwards, we conducta user survey to investigate the features of web APIs that users often consider when shortlisting a web API for testing before they adopt it, validate the identified types of web API issues, and understand users' expectations on the development and management of web APIs. From the 191 received responses, we extract 14 important features for users to decide whether to use a web API (e.g., well-organized documentation). We also gain a better understanding of web API issue types and summarize 11 categories of user expectations on web APIs (e.g., documentation and SDK/library). As the result of our study, we provide guidelines for web API developers and registry managers to improve web APIs and promote the use of web APIs.