# Ontological Representation of Smart City Data: From Devices to Cities
## 5 Conclusions and Future Work  
In this paper, a systematic literature review of smart city ontologies has been presented. The review reveals some gaps in the ontologies available for this field. First, there are smart city ontologies that are not available, a fact that completely hinders their reuse. Second, each ontology provides its custom model adapted to its specific needs, which makes it difficult to increase the interoperability among models, beyond common points, such as the modeling of time and units of measurement, where standards and well-known ontologies are usually reused. Third, some ontologies do not provide a clear documentation or the ontology requirements specification from which they are built.  
This review aimed to answer the research question defined in Section 2.1 (What are the common ontology design patterns used in smart city ontologies?). As a result, a set of ontology design patterns has been proposed. These patterns materialize the domains and requirements that a smart city should represent. These seven patterns have been designed with detailed graphical conceptualizations, use cases, and suggestions about how they may be implemented, including links to the ontologies that can fit their requirements. In addition, these patterns are inspired and therefore aligned with the inspected ontologies, shown in Table 3, as well as the ontologies commonly reused by them, shown in Table 4. As a result, a core model for smart cities has been provided in order to improve the interoperability and ease the development of these kinds of ontologies.  
An important aspect of the proposed ODP is the alignment with existing standards and well-known models for smart city data. Due to the fact that the proposed ODPs are based on the ontological requirements that have been obtained from standards such as \"ISO 37120\" and the \"AENOR norm UNE 178301:2015\", and broadly-used models like FIWARE, the ISA2 ontologies, etc., it is expected to achieve broader interoperability than the models designed for a particular use case.  
As future work, the proposed patterns may be encoded in an ontology implementation language such as OWL ([[https://www.w3.org/OWL](https://www.w3.org/OWL)]([https://www.w3.org/OWL](https://www.w3.org/OWL))), and it may be submitted to the Ontology Design Pattern catalog. In addition, these patterns are being implemented in an ontology under development for smart cities. Moreover, it may be interesting to reach an agreement with other patterns from domains not covered in this work. Finally, a set of guidelines and examples may be provided in order to explain how to extend these patterns or how to use them with data.  
Conceptualization, M.P.-V., O.C., P.E.-A., and R.G.-C.; methodology, M.P.-V., P.E.-A., and R.G.-C.; validation, M.P.-V., and R.G.-C.; investigation, P.E.-A.; writing, original draft preparation, M.P.-V. and P.E.-A.; writing, review and editing, M.P.-V., O.C., P.E.-A., and R.G.-C.; supervision, M.P.-V. and R.G.-C.  
This work was partially supported by a Predoctoral grant from the I+D+iprogram of the Universidad Politecnica de Madrid, ETSISpecialist Task Force 534, and DATOS4.0: RETOS Y SOLUCTIONES--UPMSpanish national project (TIN2016-78011-C4-4-R).  
The authors would like to thank the members of the ETSI Specialist Task Force 534 and of the ETSI SmartM2M Technical Committee for feedback on this work.  
The authors declare no conflict of interest.