1. A method of enhancing or suppressing measures of relationships between documents based on the relationships arising from text pertaining to selected topics, the method comprising: obtaining, with one or more processors, a corpus of more than 500 documents, each document having unstructured natural language text; obtaining, with one or more processors, a set of topics and, for each topic in the set, a respective set of n-grams pertaining to the respective topic; receiving, with one or more processors, a selected topic among the set of topics, the selection indicating that relationships between the documents are to be enhanced or suppressed in virtue of the relationships arising from text relating to the selected topic; forming, with one or more processors, a relationship graph of the documents, the relationship graph having more than 500 nodes, each node corresponding to at least one document, the graph having edges between nodes indicating a relationship between documents corresponding to the respective nodes, wherein: forming the relationship graph comprises forming a feature vector for each document, each feature vector having plurality of scores, each score corresponding to a given n-gram and being based on: an amount of occurrences of the given n-gram in the respective document, a length of the respective document, an amount of occurrences of the given n-gram in a plurality of other documents different from the respective document, and whether the given n-gram is among the set of n-grams pertaining to the selected topic and, when the given n-gram pertains to the selected topic, a cardinal score indicating an amount that the given n-gram pertains to the selected topic, the relationships between pairs of the documents are determined based on co-occurrence of n-grams in the pairs of the documents, and wherein the relationships are enhanced or suppressed in response to co-occurring n-grams being in the respective set of n-grams of the selected topic; and storing the relationship graph in memory.