7. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving a query from an initiating resource; determining a topic associated with the query; selecting candidate resources that are associated with the topic; determining whether the topic of the query is specified as a subjective topic or an objective topic; in response to determining that the topic of the query is specified as a subjective topic: for each of the candidate resources, determining a similarity score based on a similarity of one or more contextual factors, other than the topic, associated with the initiating resource and the candidate resource that reflects an extent to which the initiating resource and the candidate resource are similar; obtaining a response to the query from a first candidate resource that has a similarity score that satisfies one or more predetermined criteria; and providing, to the initiating resource, the response to the query that is obtained from the first candidate resource that has a similarity score that satisfies the one or more predetermined criteria; and in response to determining that the topic of the query is specified as an objective topic: obtaining a response to the query from a second candidate resource regardless of similarity of the one or more contextual factors between the initiating resource and each of the candidate resources; and providing, to the initiating resource, the response to the query that is obtained from the second candidate resource.
7. A system comprising: one or more computers and one or more storage devices storing instructions that are operable, when executed by the one or more computers, to cause the one or more computers to perform operations comprising: receiving a query from an initiating resource; determining a topic associated with the query; selecting candidate resources that are associated with the topic; determining whether the topic of the query is specified as a subjective topic or an objective topic; in response to determining that the topic of the query is specified as a subjective topic: for each of the candidate resources, determining a similarity score based on a similarity of one or more contextual factors, other than the topic, associated with the initiating resource and the candidate resource that reflects an extent to which the initiating resource and the candidate resource are similar; obtaining a response to the query from a first candidate resource that has a similarity score that satisfies one or more predetermined criteria; and providing, to the initiating resource, the response to the query that is obtained from the first candidate resource that has a similarity score that satisfies the one or more predetermined criteria; and in response to determining that the topic of the query is specified as an objective topic: obtaining a response to the query from a second candidate resource regardless of similarity of the one or more contextual factors between the initiating resource and each of the candidate resources; and providing, to the initiating resource, the response to the query that is obtained from the second candidate resource. 8. The system of claim 7 , wherein selecting candidate resources that are associated with the topic comprises identifying a set of candidate resources from a plurality of resources based on an expertise level score, for the determined topic, of each resource of the plurality of resources.