@article {apiace:2024:jwe,
	title = {How Are Web APIs Versioned in Practice? A Large-Scale Empirical Study},
	journal = {Journal of Web Engineering},
	volume = {23},
	year = {2024},
	month = {August},
	pages = {465-506 },
	abstract = {Web APIs form the cornerstone of modern software ecosystems, facilitating seamless data exchange and service integration. Ensuring the compatibility and longevity of these APIs is paramount. This study delves into the intricate realm of API versioning practices, a crucial mechanism for managing API evolution. Exploring an expanded and diverse dataset of 603 293 APIs specifications created during the 2015{\textendash}2023 timeframe and gathered from four different sources, we examined the adoption of the following versioning practices: Metadata-based, URL-based, Header-based and Dynamic versioning, with one or more versions in production. API developers use more than 50 different version identifier formats to encode information about the changes introduced with respect to the previous version (i.e., semantic versioning), about when the version was released (i.e., age versioning) and about which phase of the API development lifecycle the version belongs (i.e., stable vs. preview releases).},
	keywords = {API Analytics; API Versioning},
	doi = {10.13052/jwe1540-9589.2341},
	url = {https://journals.riverpublishers.com/index.php/JWE/article/view/26595/20349},
	author = {Souhaila Serbout and Cesare Pautasso}
}
@conference {apiace:2024:icwe,
	title = {How Many Web APIs Evolve Following Semantic Versioning?},
	booktitle = {24th International Conference on Web Engineering (ICWE)},
	year = {2024},
	month = {June},
	publisher = {Springer},
	organization = {Springer},
	address = {Tampere, Finland},
	abstract = {More and more Web APIs use semantic versioning to represent the impact of changes on clients depending on previous versions. Our goal is to provide insights about the extent to which evolving Web APIs align with semantic versioning rules. In this paper we present the results of an empirical study on the descriptions of 3 075 Web APIs, which released at least one new version throughout their history. The APIs descriptions were mined by retrieving 132 909 commits from 2 028 different open source GitHub repositories. We systematically collected and examined 506 273 changes of 195 different types released within 16 053 new API versions. We classified whether each change is likely to break clients or not, and checked whether the corresponding version identifier has been updated following semantic versioning rules. The results indicate that in the best case, only 517 APIs consistently release major upgrades when introducing breaking changes, while 1 970 APIs will not always correctly inform their clients about breaking changes released as part of minor or patch-level upgrades. We also detected 927 APIs which use a backwards-compatible evolution strategy, as they never introduce any breaking change throughout their history.},
	keywords = {API Analytics, API Evolution, Semantic Versioning, Web API},
	doi = {10.1007/978-3-031-62362-2_25},
	url = {https://link.springer.com/chapter/10.1007/978-3-031-62362-2_25},
	author = {Souhaila Serbout and Cesare Pautasso}
}
@conference {apiace:2022:icws,
	title = {How Composable is the Web? An Empirical Study on OpenAPI Data model Compatibility},
	booktitle = {IEEE World Congress on Services (ICWS Symposium on Services for Machine Learning)},
	year = {2022},
	month = {July},
	pages = {415-424},
	publisher = {IEEE},
	organization = {IEEE},
	address = {Barcelona, Spain},
	abstract = {Composing Web APIs is a widely adopted practice by developers to speed up the development process of complex Web applications, mashups, and data processing pipelines. However, since most publicly available APIs are built independently of each other, developers often need to invest their efforts in solving incompatibility issues by writing ad-hoc glue code, adapters and message translation mappings. How likely are Web APIs to be directly composable?

The paper presents an empirical study to determine the potential composability of a large collection of 20,587 public Web APIs by verifying their schemas{\textquoteright} compatibility. We define three levels of data model elements compatibility -- considering matches between property names and/or data types -- which can be determined statically based on API descriptions conforming to the OpenAPI specification. The study research questions address: to which extent are Web APIs compatible; the average number of compatible endpoints within each API; the likelihood of finding two APIs with at least one pair of compatible endpoints. 

To perform the analysis we developed a compatibility checker tool which can statically determine API schema compatibility on the three levels and find matching pairs of API responses which can be directly forwarded as requests to the same or other APIs. We run the tool on a dataset of 751,390 request and response message schemas extracted from publicly available OpenAPI descriptions.

The results indicate a relatively high number of compatible APIs when matching their data models only on the level of their elements{\textquoteright} data type. However, this number gets lower narrowing the scope to only the ones handling data objects having identical properties name. The average likelihood of finding two compatible APIs with both matching property names and data types reaches 21\%. Also, the number of compatible endpoints within the same API is very low.},
	keywords = {API Analytics, empirical study, mashups, OpenAPI, Web APIs},
	doi = {10.1109/ICWS55610.2022.00068},
	author = {Souhaila Serbout and Cesare Pautasso and Uwe Zdun}
}
