1. A method, comprising: receiving, by a context analysis module, annotated documents, the annotated documents comprising annotated fields; analyzing, by the context analysis module, the annotated documents to determine contextual information for each of the annotated fields; determining discriminative sequences using the contextual information, wherein determining discriminative sequences further comprises: determining, by a contiguity heuristics module, longest contiguous common subsequences between aligned pairs of strings of the annotated documents; determining, by the contiguity heuristics module, a frequency of occurrence of similar longest contiguous common subsequences; and wherein the contiguity heuristics module generates a proposed rule or a feature set from longest contiguous common subsequences having a desired frequency of occurrence; generating, by the context analysis module, the proposed rule or the feature set using the discriminative sequences and the annotated fields; providing, by the context analysis module, the proposed rule or the feature set to a document annotator; converting, by a feature-based extractor generator, the feature set into a feature-based vector; and applying, by a classifier model annotator, the feature-based vector to a target document to create an annotated document.