  There are several aspects of data markets that distinguish them from a
typical commodity market: asymmetric information, the non-rivalrous nature of
data, and informational externalities. Formally, this gives rise to a new class
of games which we call multiple-principal, multiple-agent problem with
non-rivalrous goods. Under the assumption that the principal's payoff is
quasilinear in the payments given to agents, we show that there is a
fundamental degeneracy in the market of non-rivalrous goods. This multiplicity
of equilibria also affects common refinements of equilibrium definitions
intended to uniquely select an equilibrium: both variational equilibria and
normalized equilibria will be non-unique in general. This implies that most
existing equilibrium concepts cannot provide predictions on the outcomes of
data markets emerging today. The results support the idea that modifications to
payment contracts themselves are unlikely to yield a unique equilibrium, and
either changes to the models of study or new equilibrium concepts will be
required to determine unique equilibria in settings with multiple principals
and a non-rivalrous good.
