1. A system for retrieving/identifying a document comprising text stored in a document repository comprising: a memory storing a graphical structure comprising a first plurality of nodes each representing a person, and a second plurality of nodes each representing a document in the document repository, the nodes being connected by edges according to automatically observed interactions between the represented people and documents, at least some of the nodes having one or more annotations each denoting a topic; a node relatedness calculator arranged to compute distances between nodes of the graphical structure using the topic annotations; an input arranged to receive at least an identifier of a user who is represented by one of the first plurality of nodes; and an identifier/retriever arranged to identify one or more documents from the document repository by using the identifier and using the computed distances between nodes.