From Bioinformatics.Org Wiki
Biology is changing from being a descriptive to an analytical science. Accurate and consistent descriptions are, however, vital to analysis. The idea of ontologies has been co-opted from philosophy and artificial intelligence to partition bioinformatic knowledge in a way which can be reliably navigated by computers.
[resources/Holloway02.pdf This preprint] of a review by Ele Holloway of the European Bioinformatics Institute gives a more detailed insight into the varied approaches to ontologies in bioinformatics by covering a recent meeting on the subject. The final version appears in Comparative and Functional Genomics.