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 by: 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 from longest contiguous common subsequences having a desired frequency of occurrence; providing, by the context analysis module, the proposed rule to a document annotator; and applying, by a rule-based annotator, a rule-based extractor to a target document to create an annotated document, the rule-based extractor being generated from the proposed rule.