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.