1. A method, comprising: providing a data store including documents; providing a semantic model including a plurality of concepts, wherein the semantic model is derived at least in part from a reference source that includes content not included in the data store; determining at least one similarity metric for each document of the plurality of documents, wherein each respective similarity metric represents a similarity between a respective document of the plurality of documents and a respective concept of the plurality of concepts in the semantic model; receiving a search query; computing at least one relevance metric of the search query, wherein each relevance metric represents a relevance of the search query to a respective concept of the plurality of concepts represented in the semantic model; and determining a ranking of at least a subset of the plurality of documents with respect to the search query using at least the at least one similarity metric and the at least one relevance metric.