## 4 Experimental Results
### Domain-Oriented Ontological Model and Data Visualization Artifact  
This research demonstrates the advanced development process of a focus ontology based on Cardiovascular Diseases (CVO) while capturing the contextual knowledge of healthcare units within healthcare organizations. The ontology development process follows a top-to-bottom modular approach combining, aligning, and extending predefined ontologies relevant to the CVO and healthcare domains. _Ontological Blueprint and Creation:_ We showcase the construction of the CVO ontology and its systematic process in Figure 4, emphasizing the sequential phases involved in building the system architecture needed to create federated IS. This phase also contributes to building FO and constituting the domain ontological model, and it consists of injecting data into the ontology OWL file using the OPE method. This section further explains the foundation for building domain ontologies, which serve specific purposes, reflect a particular domain, and define the activities to be included. We utilized mature methodologies for developing ontologies, such as Methontology [63] and Tove [64] methodologies. We used a customized approach to develop FO, integrating domain knowledge, contextual insights from domain experts, and external domain knowledge through the OPE method by fetching data from various data models and mapping into the FO. Figure 4 below showcases the ontological model taxonomies and outlines ontology visualization. _Top-to-bottom Modular Approach for Ontology Construction:_ In this phase, we employed various relevant ontology development methods such as Methontology and Tove. We customized certain activities of these methods to develop a robust framework for incorporating contextual knowledge regarding CVO. The customized hybrid approach helps build the FO ontological model (the model contains information mapped from various sources). The CVO ontological model proposed the foundational ontological meta-model for constructing federated information systems. It highlights a multidisciplinary application in which we \begin{table}
\begin{tabular}{l} \hline \hline \multicolumn{2}{c}{**Mapping Rules**} \\ \hline
**Rule 1:** Tables in databases are to be associated with OWL classes in ontology file. \\
**Rule 2:** Handling of bridge tables using constraint keys. \\
**Rule 3:** Mapping of referential integrity relationships to inheritance hierarchy. \\
**Rule 4:** Mapping of non-referential integrity columns into datatype properties. \\
**Rule 5:** Represents data type properties in the host class as Domain (D) and data type as Range (R). \\
**Rule 6:** Mapping relationships represented by referential integrity columns into object properties. \\
**Rule 7:** Representation of object property host classes as D and R. \\
**Rule 8:** All table records are mapped to individuals in ontology. \\
**Rule 9:** Database column constraints are mapped into ontology property cardinalities [68]. \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Relational database to ontology mapping rules. followed a modular approach for heavy-weight ontology construction with domain-centric axioms and their populations. Merging, Aligning, and Extending for Federated OntologyIn the process of FO, we demonstrate a conceptual view of merging the ontological model of CVO and contextual knowledge and mapping external knowledge from different data models using the OPE method. At the same time, Ontop provides a platform for creating a virtual environment by integrating various internal and external relational data sources, along with knowledge consolidated in the FO. The federated knowledge is accumulated in the federated ontology, enabling virtualization capabilities. The federated ontology consolidates data results mapped from various relational databases, seed ontology, and data models without data movement or migration, resulting in a lower latency rate. The federated data are eligible for exchange with a standardized RDF format for developing different data-driven applications.