1. A computer-implemented method comprising: receiving, by an entity extraction computer, from a client computer a search query comprising one or more entities; comparing, by the entity extraction computer, each respective entity with one or more co-occurrences of the respective entity in a co-occurrence in-memory database, wherein the co-occurrence database comprises one or more entries for the one or more entities, and wherein each entry for the respective entity of the one or more entities contains a semantically-related entity that identifies the respective entity, and wherein the co-occurrence is an instance of an entity of the one or more entities identified by the semantically-related entity in the corpus of documents in the co-occurrence database, and wherein the semantically-related entity corresponds to a model indicating distinct entities; extracting, by the entity extraction computer, a subset of the one or more entities from the search query responsive to determining each respective entity of the subset exceeds a confidence score of the co-occurrence database based on a degree of certainty of co-occurrence of the entity with one or more related entities in an electronic data corpus according to the co-occurrence database; assigning, by the entity extraction computer, an index identifier (index ID) to each of the entities in the plurality of extracted entities; disambiguating, by the entity extraction computer, each of the entities in the plurality of extracted entities from one another based on relatedness of index IDs; identifying, by the entity extraction computer, a subset of entities associated with each of the entities in the plurality of extracted entities based on relatedness of index IDs; linking, by the entity extraction computer, each entity to the associated subset of entities based at least on confidence scores; saving, by the entity extraction computer, the index ID for each of the plurality of extracted entities in the electronic data corpus, the electronic data corpus being indexed by an index ID corresponding to each of the one or more related entities; searching, by a search server computer, the entity indexed electronic data corpus to locate the plurality of extracted entities and identify index IDs of data records in which at least two of the plurality of extracted entities co-occur; and building, by the search server computer, a search result list having data records corresponding to the identified index IDs.