1. A method comprising: crawling, via an entity extraction computer, a corpus of electronic documents; extracting, via the entity extraction computer, a plurality of features from each of the crawled documents in the corpus; aggregating, via a knowledge base aggregator computer, instances of co-occurrence of two or more of the plurality of features across the crawled documents to determine a count of the instances of co-occurrence; and adding, via the knowledge base aggregator computer, an instance of co-occurrence of the two or more features to a feature co-occurrence database when the count of the instances of co-occurrence exceeds a predetermined threshold.