Relations between Ontologies
In the previous section, we have shown operations that relate ontologies. A classification of the degree of translatability between two ontologies is provided in FIPA Ontology Service Specification:
- Extension - ontology O1 extends ontology O2. The ontology O1 extends or includes the ontology O2. Informally this means that all the symbols that are defined within the O2 are found in the O1 together with the restrictions, meanings and other axiomatic relations of these symbols from O2.
- Identical - ontologies O1 and O2 are identical. Vocabulary, axiomatization and the language are physically identical, but the name can be different.
- Equivalent - ontologies O1 and O2 are equivalent. Logical vocabulary and logical axiomatization are the same, but the language (syntax) is different. When O1 and O2 are equivalent then they are strongly translatable in both ways.
- Strongly-translatable - source ontology O1 is strongly translatable to the target ontology O2. The vocabulary of O1 can be totally translated to the vocabulary of O2, axiomatization from O1 holds in O2, there is no loss of information from O1 to O2 and there is no introduction of inconsistency. Note that the representation languages can still be different.
- Weakly-translatable - source ontology O1 is weakly translatable to the target ontology O2. The translation permits some loss of information (e.g. the terms are simplified in O2), but doesn't permit introduction of inconsistency.
- Approx-translatable - source ontology O1 is approximately translatable to the target ontology O2. The translation permits even introduction of inconsistencies, i.e. some of the relations become no more valid and some constraints do not apply anymore.
Like with the operations in the previous section, deciding the relationship between two ontologies often requires manual intervention. Also, one is usually interested also in the way of translating between translatable ontologies. Once the relationship is known, it can be used for deciding what ontologies to select for particular purposes.