The four expression ontologies are used to annotate cDNA clone libraries. ESTs can be transitively associated with ontology terms via their association with a unique clone library. Clone libraries are generated from biological sample materials representing specific expression states (e.g., human foreskin fibroblasts). All of the genes/transcripts expressed in the original biological sample are captured in the clone library and can be sequenced as ESTs from the library. By mapping the clone libraries to a set of controlled terms (the ontologies), all of the ESTs from each clone library can be transitively linked to these same standardized terms in the relevant ontology via their association with their parent clone library.
