28. The system of claim 23 , wherein selecting a web resource referenced by a particular search result of the obtained search results as relevant additional content for the first web resource comprises: generating a first score for each of one or more of the identified central entities based at least in part on weights of outgoing edges of respective nodes corresponding to the identified central entities; determining that the particular search result was identified as being responsive to a search query generated for a central entity having a highest first score among the one or more identified central entities; and selecting a web resource referenced by the particular search result.
28. The system of claim 23 , wherein selecting a web resource referenced by a particular search result of the obtained search results as relevant additional content for the first web resource comprises: generating a first score for each of one or more of the identified central entities based at least in part on weights of outgoing edges of respective nodes corresponding to the identified central entities; determining that the particular search result was identified as being responsive to a search query generated for a central entity having a highest first score among the one or more identified central entities; and selecting a web resource referenced by the particular search result. 30. The system of claim 28 , wherein the first score for the particular identified central entity is based at least in part on a frequency of occurrence of the identified central entity in the first resource.