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Discover whether to merge ontologies or reason them independently in OWL. Learn the best practices to effectively use reasoners like Hermit with your ontologies.
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Understanding Ontology Reasoning with OWL: Merging vs. Independent Reasoning

In the world of ontologies, particularly when working with OWL (Web Ontology Language), one common challenge developers face is deciding how to effectively reason with multiple ontologies. If you've loaded several ontologies in a single OWLOntologyManager instance, you may wonder whether merging them is necessary for effective reasoning or if you can treat them independently. This guide aims to clarify this aspect and guide you through the best practices for ontology reasoning using popular reasoners like Hermit.

Problem Statement

Imagine you are working with three ontologies: o1, o2, and o3. The relationships between these ontologies are hierarchical, where:

o2 imports o1.

o3 imports o2.

The goal is to reason over o3 using the Hermit reasoner so that the inferred facts take into account the axioms from o1 and o2 as well. The key question arises: Should you merge all three ontologies into a new one, or can you reason over these ontologies independently?

Solution Explained

The Independent Reasoning Approach

The good news is that it's sufficient to use o3 as the sole argument for creating the reasoner. Here's why:

Automatic Usage of Imports: When you create a reasoner with o3, it automatically utilizes the imported ontologies (o1 and o2) to carry out reasoning. This means that any axioms present in o1 and o2 that are relevant to o3 will be considered without needing to merge all three ontologies into a single file.

Advantages of Not Merging

Reasons to opt for independent reasoning rather than merging include:

Simplicity: Maintaining separate ontologies avoids the complexity of managing a merged ontology and ensures that any updates made to individual ontologies can be reflected without the need for constant re-merging.

Performance: Depending on the use case and size of the ontologies, reasoning over smaller, independently managed ontologies may lead to enhanced performance and quicker inference times.

Clarity: Keeping ontologies separate may help in better organization and understanding of the relationships and definitions, especially in large and intricate projects.

Reasoning Flow

Here’s how you can set up your reasoner while ensuring that all necessary data is taken into account:

Instantiate the Reasoner: Create the Hermit reasoner with o3.

Execute Reasoning: Request reasoning to infer new knowledge based on the axioms of o3, while the imports from o1 and o2 are handled automatically.

Retrieve Inferences: Extract the inferred facts from the reasoner based on the connected ontologies.

Conclusion

In conclusion, there is no need to merge your ontologies o1, o2, and o3 into a single entity to effectively reason over o3. By leveraging the import structure within OWL and utilizing Hermit, you can achieve the desired inferences while maintaining the individual integrity of your ontologies. This approach not only simplifies your workflow but also takes full advantage of the hierarchical relationships established within your data.

Incorporating best practices when managing ontologies is crucial for efficient semantics processing, and understanding how to leverage the power of reasoners will serve you well in the long run.