1. A computer-implemented method comprising: defining a set of reduced regular expressions for particular patterns in strings, wherein the set of reduced regular expressions has less expressiveness than a set of regular expressions; and learning, from a training set, a knowledge base that uses the reduced regular expressions to resolve ambiguity based upon the strings in which the ambiguity occurs, wherein the learning includes transformation sequence learning to create a set of rules that use the reduced regular expressions to resolve ambiguity based upon the strings in which the ambiguity occurs.