The contest associated with the Topical Classification of Biomedical Research Papers conference involves the use of of the domain ontology MeSH. The contest involves the classification of materials using that ontology and clustering the results. (You should read the contest description for the full details. I am only pulling out facts needed for this post, which aren’t many.)
It occurred to me that an ontology consists of a set of values that are semantically discrete. That is any value in an ontology is distinct from all other values in the ontology and there is no “almost X,” or “nearly Y,” in an ontology.
I mention this because we apply ontologies to semantically continuous domains. Such as journal articles that were written without regard to any particular ontology.
Which would also explain why given a common ontology, such as MeSH, we may disagree as to which terms to apply to a particular document. We “see” different aspects in the semantically continuous document that influence our view of what term from the semantically discrete ontology to use. And in many cases we may be in agreement.
But the fact remains that we have applied a semantically discrete instrument to a semantically continuous data set.
I suppose one question is whether rough sets can capture and preserve some semantic continuity for use in information retrieval.