Due to the huge amount of data published on the Web, the Web search process has become more difficult, and it is sometimes hard to get the expected results, especially when the users are less certain about their information needs. Several efforts have been proposed to support exploratory search on the web by using query expansion, faceted search, or supplementary information extracted from exte...

This essay surveys the literature on directed search and competitive equilibrium, covering theory a variety of applications. These models share features with traditional theory, but also differ in important ways. They general equilibrium explicit frictions. Equilibria are often efficient, mainly because markets price goods plus time required to get them. The approach is tractable arguably reali...