1. A method for automatically extracting structure-related data from semi-structured input documents, the method comprising: receiving at a data extraction system an input document for processing; converting by a processor in the data extraction system the input document to a hypertext markup language (HTML) representation that includes a plurality of HTML tags; detecting by the processor a recurring pattern of HTML tags within the input document; inferring by the processor a structure of the input document comprising a relationship between content sections in the input document based on the recurring pattern of HTML tags; and storing a representation of the inferred structure of the input document in a repository accessible by the data extraction system.