1. A product comprising: a non-transitory 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 for execution by a processor, the logic comprising: document structure instance identification logic configured to cause the processor to: identify a first document structure instance and a second document structure instance in a document; classification logic configured 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, wherein a horizontal relationship exists between the first classification and the second classification such that neither of the first and second classifications are ancestors of the other; and instance relationship analysis logic configured to cause the processor to: analyze the class definition relationships to determine whether a change in the first classification affects the second classification, and based on the analysis, output an analysis result that indicates whether the first classification affects the second classification, wherein the analysis result facilitates determining whether conflicts exist between the first and second document structure instances of the document, which in turn facilitates improving an accuracy, completeness, and clarity of the document.