The Discipline of Organizing: Professional Edition, 4th Edition

8.6. Computational Classification

Because of its importance, ubiquity, and ease of processing by computers, it should not be surprising that a great many computational classification problems involve text. Some of these problems are relatively simple, like identifying the language in which a text is written, which is solved by comparing the probability of one, two, and three character-long contiguous strings in the text against their probabilities in different languages. For example, in English the most likely strings are “the”, “and”, “to”, “of”, “a”, “in”, and so on. But if the most likely strings are “der”, “die”, “und”, and “den” the text is German and if they are “de”, “la”, “que”, “el”, and “en” the text is Spanish.

More challenging text classification problems arise when more features are required to describe each instance being classified and where the features are less predictable. The unknown author of a document can sometimes be identified by analyzing other documents known to be written by him to identify a set of features like word frequency, phrase structure, and sentence length that create a “writeprint” analogous to a fingerprint that uniquely identifies him. This kind of analysis was used in 2013 to determine that Harry Potter author J. K. Rowling had written a crime fiction novel entitled The Cuckoo's Calling under the pseudonym Robert Galbraith.514[Com]

Another challenging text classification problem is sentiment analysis, determining whether a text has a positive ...