12. A system, comprising: a processor; and logic encoded in one or more tangible media for execution by the processor, the logic when executed by the processor causing the system to perform operations comprising: receiving annotated documents comprising annotated fields; analyzing 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, wherein the contiguity heuristics module generates a proposed rule from longest contiguous common subsequences having a desired frequency of occurrence, wherein the proposed rule is generated using the discriminative sequences, the annotated fields and a feature set; and providing the proposed rule or the feature set to a document annotator; and wherein a rule-based annotator applies a rule-based extractor to a target document to create an annotated document, the rule-based extractor being generated from the proposed rule.
14. The system of claim 12 , wherein the processor further executes the logic to perform operations of: executing a base annotation of original documents to create documents with base annotations, the base annotations comprising basic categories of words or groups of characters; and providing the documents with base annotations to the document annotator via a user interface.