Learning with Exposure Constraints in Recommendation Systems

Recommendation systems (RSs) are the principal ingredient of many online services and platforms like Youtube, Quora, Substack, and Medium. Algorithmicall y, those platforms treat the task of recommendation as a matching problem. RSs match a user's con text, i.e., their past interactions, demographics, etc., to an item from a predetermined list of i tems, e.g., news articles, which will hopefully satisfy that user. The quality of a user-content m atch is initially unclear, so many data-driven approaches have been proposed to determine a matchin g's quality; for instance, collaborate filtering [ 23 ], matrix completion [ 37 ], and online learning [ 7 ]. However, due to their rapid adoption in commercial applications, many RSs are now dynamic economic systems with multiple stakeholders, facing challenges beyond dissolving uncertainty in matchi ng. Fairness [ 6, 15, 18, 35 ], misinformation [ 17 ], user incentives [ 3, 24 ], and privacy [ 21 ] are only some of the challenges RSs face. A recent body of research addresses tradeoffs among stakehol ders [ 9, 10, 28 ]. Online platforms have three main stakeholders: The commercial company that r uns the platform, content consumers, and content providers. Content consumers, which we refer to as users for simplicity, enjoy the RSs' content.