How can I obtain confidence that an ontology is correct?

A good place to start is to run an inference engine to see if there an any logical inconsistencies or classes that cannot possibly have any members. The former is always an error; the latter usually leads to an error. However, this is only the beginning. Plenty of errors can remain even when the ontology passes the above tests. Another good thing to do is to examine the inferred hierarchy to ensure that everything makes sense. When it does not, click to get an explanation and then track down the error. Another important technique is to create unit test data. Often an error will not show up until it is run against data. Creating test data is also a good way to test your understanding of the model; it is where the rubber hits the road. It is easy to think a portion of the ontology is right, only to find gaps and errors when creating test triples. Look at alphabetized lists of classes and properties to find likely spelling errors. You can also identify patterns that you know to be likely errors and write SPARQL queries to find them. For example, if you like to have inverses for all your object properties, you can easily find exceptions this way. Many of the most common pitfalls have been already identified and code has been written to find them; see: “Are there any tools to help find common pitfalls in ontologies?” Finally, you should check the ontology against the sources of knowledge. If you interviewed some experts, show and explain the ontology to them for feedback.