Leveraging Entities in Document Retrieval

This chapter focuses on the classic problem of ad hoc document retrieval and discusses how entities may be leveraged to improve retrieval performance. Entities facilitate a semantic understanding of both the user’s information need, as expressed by the keyword query, and of the document’s content. We present three different families of approaches: (1) expansion-based methods, which utilize entities as a source of expansion terms to enrich the representation of the query; (2) projection-based methods, which treat entities as a latent layer, while leaving the original document/query representations intact; and (3) entity-based methods, which consider explicitly the entities that are recognized in documents, and embrace entity-based representations in “duet” with traditional term-based representations.