Designing a Semantic API for Open City Data

Many countries currently maintain a national data catalog, which provides access to theavailable datasets – sometimes via an Application Programming Interface (API). These APIs play acrucial role in realizing the benefits of open data as they are the means by which data isdiscovered and accessed by applications that make use of it. This article proposes semantic APIsas a way of improving access to open data. A semantic API helps to retrieve datasets according totheir type (e.g., sensor, climate, finance), and facilitates reasoning about and learning fromdata. In order to inform the design of such an API, the article explores the different categoriesof datasets made available in 40 European open data catalogs. The results show that theprobability of inter-country agreement between open data catalogs is less than 30 percent, andthat few categories stand out as candidates for a transnational semantic API.