  We investigate the application of the Shapley value to quantifying the
contribution of a tuple to a query answer. The Shapley value is a widely known
numerical measure in cooperative game theory and in many applications of game
theory for assessing the contribution of a player to a coalition game. It has
been established already in the 1950s, and is theoretically justified by being
the very single wealth-distribution measure that satisfies some natural axioms.
While this value has been investigated in several areas, it received little
attention in data management. We study this measure in the context of
conjunctive and aggregate queries by defining corresponding coalition games. We
provide algorithmic and complexity-theoretic results on the computation of
Shapley-based contributions to query answers; and for the hard cases we present
approximation algorithms.
