1. A method for use with at least one keyword retrieved from a first set of documents related to a predefined subject matter, the method comprising: constructing snippets from textual material in said first set of documents, each of said snippets including at least one word appearing within a specified text distance of said at least one keyword; defining a plurality of categories wherein each of said snippets is assigned to one of said categories, each of said categories designated for receiving similar snippets; creating a respective mathematical model for each of said categories; analyzing a second set of documents to determine an assignment for each document in said second set of documents to one of said categories, said assignment based on matching each of said documents in said second set of documents to said mathematical model for said assigned category; and identifying at least one white space in said second set of documents, said at least one white space including fewer than a specified number of documents.