For a fixed retrieval model that satisfies users’ information need to some extent
Margin: a unit of incremental data size may increase the “dimension” of the data, which makes it more difficult for the model to handle. Thus non-positive margin.
For a fixed data producing model that provides “information supply”.
Margin: a unit of incremental data size may increase the “dimension” of the data. In this situation, a new “basis” can be used to generate more “new deep” data. Thus non-negative margin.
Intersection: the best performance(utility) bound for a fixed retrieval model and data generator.