1. A method for performing schema-validation of a document, said method comprising the steps of: defining a schema; defining a set of constraining rules associated with said schema, said set of constraining rules identifying at least one valid change for at least one of an attribute and an element of said schema; parsing said document using a rule-based parser associated with said set of constraining rules; and determining a similarity score for said document with respect to said schema, based on said parsing.