  Background: Single-Subject Design is used in several areas such as education
and biomedicine. However, no suited formal vocabulary exists for annotating the
detailed configuration and the results of this type of research studies with
the appropriate granularity for looking for information about them. Therefore,
the search for those study designs relies heavily on a syntactical search on
the abstract, keywords or full text of the publications about the study, which
entails some limitations. Objective: To present SSDOnt, a specific purpose
ontology for describing and annotating single-subject design studies, so that
complex questions can be asked about them afterwards. Methods: The ontology was
developed following the NeOn methodology. Once the requirements of the ontology
were defined, a formal model was described in a Description Logic and later
implemented in the ontology language OWL 2 DL. Results: We show how the
ontology provides a reference model with a suitable terminology for the
annotation and searching of single-subject design studies and their main
components, such as the phases, the intervention types, the outcomes and the
results. Some mappings with terms of related ontologies have been established.
We show as proof-of-concept that classes in the ontology can be easily extended
to annotate more precise information about specific interventions and outcomes
such as those related to autism. Moreover, we provide examples of some types of
queries that can be posed to the ontology. Conclusions: SSDOnt has achieved the
purpose of covering the descriptions of the domain of single-subject research
studies.
