An API is an importable symbol from a (standard) library, e. g. node:fs.mkdir,
net/http.NewRequest or urllib.parse.
A catalogue is a collection of meta information. For APIs, it contains the amount of APIs, the amount of namespaces, namespaces symbols and technlogy version. For contributions, it contains the amount of contributions and repositories.
A contribution is an open-source file that contains location information (locus), uniquely identifiable repository information, the source code, file name, and file path.
A locus is part of contribution and consists of an API and a line number of its occurrence.