Investigating Web APIs on the World Wide Web

The world of services on the Web, thus far limited to "classical" Web services based on WSDL and SOAP, has been increasingly marked by the domination of Web APIs, characterised by their relative simplicity and their natural suitability for the Web. Currently, the development of Web APIs is rather autonomous, guided by no established standards or rules, and Web API documentation is commonly not based on an interface description language such as WSDL, but is rather given directly in HTML as part of a web page. As a result, the use of Web APIs requires extensive manual effort and the wealth of existing work on supporting common service tasks, including discovery, composition and invocation, can hardly be reused or adapted to APIs. Before we can achieve a higher level of automation and can make any significant improvement to current practices and technologies, we need to reach a deeper understanding of these. Therefore, in this paper we present a thorough analysis of the current landscape of Web API forms and descriptions, which has up-to-date remained unexplored. We base our findings on manually examining a body of publicly available APIs and, as a result, provide conclusions about common description forms, output types, usage of API parameters, invocation support, level of reusability, API granularity and authentication details. The collected data provides a solid basis for identifying deficiencies and realising how we can overcome existing limitations. More importantly, our analysis can be used as a basis for devising common standards and guidelines for Web API development.