1. A system including one or more processors implementing processing modules comprising: an activity tracking module, within a network-based transaction system, to receive and process a selected entity, the selected entity published on the network-based transaction system; a relationship module, within the network-based transaction system, to determine a plurality of related entities based at least in part on aggregated navigation transitions between the selected entity and each related entity of the plurality of related entities; and a recommendation engine, within the network-based transaction system, to generate a recommendation set of related entities, for publication via the network-based transaction system over a network connection, from the plurality of related entities based at least in part on a velocity for each related entity of the plurality of related entities, the velocity comprises a measure of directional change in popularity, and to generate the recommendation set by calculating a relevance score for each related entity in a second plurality of related entities, the relevance score is a function of probability and velocity.