Can anybody provide me with a definition of "oracle information" as it's used in NLP and machine learning? I've come across the term in in sentiment analysis, wsd, mt, and in a number of other areas but haven't been able to find a definition of the term. Here is some context:
In a section of a thesis dealing with automated classification of discourse relations, the author describes oracle information in terms that are indistinguishable from "supervised." To predict Z, manually annotated discourse segments X and Y serve as "oracles" to the classifier.
In a paper dealing with a two-stage classification task (first classify a sentence as subjective/not subjective, then classify all subjective sentences as x or y) the tags from stage 1 are described as "oracles"--so, output from the stages of a hierarchical classifier is oracle information for later stages?
In a paper dealing with named entity recognition, the authors use word alignment information as an oracle.
So, can anyone provide a decent definition for the term along with an example?