# Ontological Representation of Smart City Data: From Devices to Cities
## 2 Research Methodology
### Planning the Review
Despite the review having included important databases, two specific journals have also been considered because they have published papers on the ontology topic. In the case of the ontology registries (indexes and catalogs), Linked Open Vocabularies (LOV) [23] was chosen because it contains general and domain ontologies, and Linked Open Vocabularies for Internet of Things (LOV4 IoT) [24] and smartcity.linkeddata.es [25] were selected because they are ontology catalogs focused on smart cities. It is worth noting that LOV is classified as an ontology index as it has indexed the ontology OWL encoding, providing search features within the registered ontologies. LOV4 IoT and smartcity.linkeddata.es are considered catalogs as they compile pointers to ontologies and classify them by domains, attaching tags, but searching within the ontology elements is not allowed. Once the sources have been specified, some search terms were defined. These terms were set based on the research question and according to the main cross-domain topics involved in smart cities, oriented toward the Internet of Things domain as one of the main technologies deployed in those cities [26]. The search was limited to the following terms: ontology, ontologies, smart city, smart cities, pattern-based, design pattern, sensor, sensors, actuator, and actuators. While carrying out the review, the particularities of each source were taken into account. In the case of databases and journals, connection words, OR and AND, were used in order to combine these terms in a search string, e.g., (\"ontology\" OR \"ontologies\") AND (\"smart city\" OR \"smart cities\"). The search strings were applied in the meta fields available in the electronic database entry points shown in Table 1. According to each source, the search strings were used in the fields: content, title, abstract, and keywords. Additionally, in the case of the databases' search, articles, books, and chapter books in English were considered. In the case of ontology registries, as already mentioned, LOV is the only one that provides a search engine to find vocabulary terms, vocabularies, or agents matching keywords and/or filters; thus, the search terms were applied on vocabulary terms. Despite that LOV4 IoT and smartcity.linkeddata.es do not provide a search engine, the search terms were applied over the domains used to classify the ontologies. In this cases, the terms \"ontology\" and \"ontologies\" were omitted from the search as they are implicit in these catalogs. In order to detect those primary studies that provide valuable information to the research question, the inclusion and exclusion criteria were defined, as shown in Table 2.  
After performing the search, all duplicate results were removed, and only one of them was kept in order to be analyzed. Taking this into account, in order to carry out the selection procedure the inclusion criteria and exclusion criteria were applied to these results. \begin{table}
\begin{tabular}{l l l l l l} \hline \hline
**Inclusion Criteria (IC)** & **Databases** & **Journals** & **LOV** & **LOV4 IoT** &
\begin{tabular}{l} **Smarctity.** \\ **linkeddata.es** \\ \end{tabular} \\ \hline Peer-reviewed studies & ✓ & ✓ & & & \\ \hline Studies published between 2012 and 2018 & ✓ & ✓ & & ✓ & \\ \hline Studies that presented ontologies for smart & ✓ & ✓ & ✓ & ✓ \\ city initiatives & ✓ & ✓ & ✓ & ✓ \\ \hline Ontology design patterns papers & ✓ & ✓ & & ✓ & \\ \hline Ontology engineering papers & ✓ & ✓ & & ✓ & \\ \hline
**Exclusion Criteria (EC)** & & & & & \\ \hline Ontologies whose code has not been & ✓ & ✓ & ✓ & ✓ & ✓ \\ published online & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Ontologies released before 2012 & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline Studies/ontologies not written in English & ✓ & ✓ & ✓ & ✓ & ✓ \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Inclusion and exclusion criteria.