## 5 Conclusions  
It has been demonstrated that the international rules for MPTs can be modelled comprehensively in an OWL ontology with DL expressivity ALCOIQ. Since the MPT rules are the most complex of the data-quality checks from an ontological point of view these results confirm the applicability of OWL for a basis of European CR data-validation checks. OWL provides many advantages to help support the devolution of the CR data-validation process and motivate the eventual federation of CR data sources. Firstly and foremost, it provides the means of formally representing the validation rules using description logic, thereby removing much of the ambiguity in natural language representation. Secondly, it removes the need for a dedicated data-validation software application, which in turn reduces development and maintenance costs. Thirdly, it unifies the validation rules with the underlying data model and provides automatic synchronisation when modifications are made. Fourthly, it provides a unique address to the ontology via the ontology URI that avoids the sorts of versioning issues experienced with distributed software. Finally, it provides an automatic reasoning functionality for DL querying of the knowledge base. In cases where the use of machine reasoning leads to performance overheads for high DL expressivities, the OWL application programme interface can be used to develop application software. Software developed in this way has direct access to the ontology axioms and can be used to emulate aspects of the reasoner at a fraction of the effort of developing dedicated software. The results remove one of the remaining hurdles to developing CR validation software based entirely on an ontology and should therefore facilitate the devolution of the data-validation process to the local level. This in turn will serve to federate harmonised CR data sets and accelerate their availability for research and healthcare-policy purposes. The next step will be to integrate the MPT ontology with those addressing other aspects of the entire set of validation rules [7] and to benchmark the performance of the ontology suite with the existing ENCR quality-check software. The aim will be to replace the latter with an ontology-based tool that can be more easily and openly maintained and developed by the user base and that can support the devolution of the data quality-checking process. **Author Contributions:** Conceptualisation, N.C.N. ; Data curation, M.F. and G.R. ; Formal analysis, N.C.N. ; Investigation, T.D. and L.N. ; Methodology, N.C.N., F.G. and C.M. ; Project administration, M.B. ; Resources, N.D.; Software, N.C.N. ; Supervision, C.M. ; Validation, R.N.C. ; Writing--original draft, N.C.N. ; Writing--review & editing, F.G., M.B., R.N.C., N.D., T.D., M.F., L.N., G.R. and C.M. All authors have read and agreed to the published version of the manuscript. **Funding:** All authors are employed by governmental or supranational entities and report no additional funding for the development of this manuscript. **Data Availability Statement:** The ontologies are available at: [[http://data.europa.eu/89h/2a110a2e-d1e2-439d-9b9f-7e2e5436](http://data.europa.eu/89h/2a110a2e-d1e2-439d-9b9f-7e2e5436) cc49]([http://data.europa.eu/89h/2a110a2e-d1e2-439d-9b9f-7e2e5436](http://data.europa.eu/89h/2a110a2e-d1e2-439d-9b9f-7e2e5436) cc49) (accessed on 4 August 2020). **Acknowledgments:** This work was partly conducted using the Protege resource, which is supported by grant GM10331601 from the National Institute of General Medical Sciences of the United States National Institutes of Health. **Conflicts of Interest:** The authors declare no conflict of interest. **Abbreviations**  
ABox  
Assertional part of a knowledge base; a set of concepts and role assertions. ALCOIQ  
A specific DL expressivity incorporating: attributive language with complex concept negation, nominals, inverse properties, and qualified cardinality restrictions. CR  
Cancer Registry; an entity that collects and analyses cancer cases.