1. A computer-implemented method comprising: identifying, by a server system comprising one or more computers, first terms based on an evaluation of a web page; identifying, by the server system, one or more related resources that are associated with the first terms, and identifying, for each related resource, one or more second terms associated with the related resource based on an evaluation of the related resource; associating, by the server system, each of (i) the first terms identified based on the evaluation of the web page and (ii) the one or more second terms respectively associated with the one or more related resources with a respective node in a directed graph; providing, by the server system, one or more connections between the nodes in the directed graph, wherein the one or more connections indicate magnitudes and directions that represent one or more relationships between (i) the first terms identified based on the evaluation of the web page, and (ii) the one or more second terms respectively associated with the one or more related resources; selecting, by the server system, a subset of the first terms based on the connections representing the one or more relationships between (i) the first terms identified based on the evaluation of the web page, and (ii) the one or more second terms respectively associated with the one or more related resources; associating, by the server system, the selected subset of the first terms with the web page; storing, by the server system and in a database, data that indicates that the selected subset of the first terms are associated with the web page; selecting, by the server system, a knowledge item from among a plurality of knowledge items based on the selected subset of the first terms that the database indicates are associated with the web page; and providing, by the server system, the selected knowledge item for display with the web page at a client device.