Ontologies and Similarity

The document summarizes key points about ontologies and measuring similarity in ontologies: 1. It discusses different types of typical ontologies like the Foundational Model of Anatomy and SNOMED CT and how they are modeled using description logics. 2. When measuring similarity between classes in ontologies, early approaches used path counting in the class hierarchy but this was problematic as it discarded much information and was sensitive to modeling artifacts. 3. Later approaches measured similarity based on the extensions of classes using set-based measures like Jaccard, but this had problems with disjointness and classes with infinite or uncountable extensions. 4. The document argues that an ideal similarity measure for ontologies needs to