16. The method of claim 1 , wherein forming the relationship graph comprises forming a semantic similarity graph by performing operations comprising: determining an adjacency matrix based on the feature vectors, wherein rows and columns of the adjacency matrix correspond to the documents, values of the feature matrix correspond to a selected-topic-adjusted semantic similarity of documents corresponding to the respective row and column of the values, and values of the feature matrix are based on angles between feature vectors of the documents corresponding to the respective row and column of the values.
16. The method of claim 1 , wherein forming the relationship graph comprises forming a semantic similarity graph by performing operations comprising: determining an adjacency matrix based on the feature vectors, wherein rows and columns of the adjacency matrix correspond to the documents, values of the feature matrix correspond to a selected-topic-adjusted semantic similarity of documents corresponding to the respective row and column of the values, and values of the feature matrix are based on angles between feature vectors of the documents corresponding to the respective row and column of the values. 17. The method of claim 16 , wherein determining a feature vector comprises determining the feature vector scores by determining an amount of occurrences of the given n-gram in the respective document based on a function having a derivative that decreases in magnitude as the amount of occurrences of the given n-gram in the respective document increases.