1. A product comprising: a machine readable memory; an ontology model stored in the memory and defining a hierarchy of document structure instance classes comprising a root class, a child class, and class definition relationships between the document structure instance classes; and logic stored in the memory comprising: document structure instance identification logic operable to: identify a first document structure instance and a second document structure instance in a document; classification logic operable to: analyze the first document structure instance against the ontology model to determine a first classification for the first document structure instance among the document structure instance classes; analyze the second document structure instance against the ontology model to determine a second classification for the second document structure instance among the document structure instance classes; and instance relationship analysis logic operable to: analyze the class definition relationships to determine whether the first classification affects the second classification, and output an analysis result that depends on whether the first classification affects the second classification.