Methods, systems, and apparatus, including computer program products for structured content ranking. In an aspect, a method determines a service requirement from terms of a query, the service requirement being one of a plurality of service requirements fulfilled by databases; determines, for each of the databases, a service requirement score for the database, the service requirement score being a measure of an ability of the database to fulfill the service requirement; selects databases based on the service requirement scores; generates data responsive to the service requirement based on the terms of the query and one or more of the selected databases; and generates, from the data identifying resources that are determined to be responsive to the query and from the data responsive to the service requirement, search results that include first search results that each identify a corresponding resource that was determined to be responsive to the query.