1. A method performed by a data processing apparatus, the method comprising: determining one or more trust relationships between a user and one or more entities based on a frequency with which the user visits one or more resources associated with the one or more entities; receiving a search query from the user; identifying one or more resources responsive to the search query, wherein each of the resources is associated with one or more annotation label terms assigned by the one or more entities; determining whether a query label term matches any of the one or more annotation label terms; identifying, for each of the one or more annotation label terms matching the query label term, a trust rank of the entity that associated the annotation label term with the resource, each trust rank indicating a level of trust for annotation label terms that are assigned by the entity, and each trust rank being based on the determined one or more trust relationships that are based on the frequency with which the user visits the one or more resources; determining a relevance score of each of one or more resources that have the annotation label term based on the respective trust rank, the relevance score indicating a degree of relevance between the respective resource and the query term; ranking each of the one or more resources based on the respective relevance scores; and providing the ranking.