Existing smart city ontologies allow representing different types of city-related data from cities. They have been developed according to different ontological commitments and hence do not share a minimum core model that would facilitate interoperability among smart city information systems. In this work, a survey has been carried out in order to study available smart city ontologies and to identify the domains they are representing. Taking into account the findings of the survey and a set of ontological requirements for smart city data, a list of ontology design patterns is proposed. These patterns aim to be easily replicated and provide a minimum set of core concepts in order to guide the development of smart city ontologies.

Public administrations handle large amounts of data in relation to their internal processes as well as to the services that they offer. Following public-sector information reuse regulations and worldwide open data publication trends, these administrations are increasingly publishing their data as open data. However, open data are often released without agreed data models and in non-reusable formats, reducing interoperability and efficiency in data reuse. These aspects hinder interoperability with other administrations and do not allow taking advantage of the associated knowledge in an efficient manner. This paper presents the continued work performed by the Zaragoza city council over more than 15 years in order to generate its knowledge graph, which constitutes the key piece of their data management system, whose main strengthen is the open-data-by-default policy. The main functionalities that have been developed for the internal and external exploitation of the city’s open data are also presented. Finally, some city council experiences and lessons learned during this process are also explained.