1. A method implemented in a data processing apparatus, comprising: receiving a query from a member of an enterprise; searching an index that includes member information of members of the enterprise and documents of the enterprise, wherein: the documents include data describing entities and entity facts related to the enterprise and relationships among the entities, and each document has a respective access control list specifying access privileges to the document for members of the enterprise; the entity facts are identified from the entities of the documents of the enterprise; each entity fact describes at least one feature of the entity, wherein the feature of the entity is a relationship between the entity and another entity and wherein each entity fact is derived from one or more corresponding documents in which the entity fact is described; and the index includes data defining access privileges to the data describing the entities and the entity facts according to respective entity fact access control lists, wherein each entity fact access control list is different from the access control lists provided for the documents of the enterprise, and each entity fact inherits an access control list of a document from which the entity fact is derived, wherein deriving the entity facts comprises selecting each document from the documents, and for the selected document: determining a first entity identified within the document; determining a second entity identified within the document; determining a relationship between the first entity and the second entity that is described within the document; and generating, as the entity fact, data describing the first entity, the second entity, and the relationship between the first entity and the second entity as described in the document: wherein multiple entity facts are derived from a selected document; determining the entity facts that are accessible to the member according to the entity fact access control lists; determining, based on member information of the member, and entity facts that are accessible to the member, search result data including data describing entities and entity facts relevant to the query; and providing search results, based on the search result data, to the member of the enterprise, the search results including data describing the entities and entity facts determined to be relevant to the query.