Added a quadraticSpline enumerated value to the interpolate attributes of the independentVarPts and independentVarRef elements (in response to a request from Geoff Brian of DSTO) and fixed a typographical error in cubicSpline attribute string. Added reference to Wikipedia article on spline interpolation.

Added a classification attribute to the reference element and added a date attribute to the modificationRecord element, at the suggestion of Geoff Brian of DSTO.

Added 2D and 3D ungridded table examples and figures and corrected a typographical error in the ungridded table definition syntax (thanks to Dr. Peter Grant of U. Toronto's UTIAS and Geoff Brian of DSTO).

Reintroduced <!ENTITY> to include MathML-2 DTD (complete) in the body of this DTD. This entity definition quietly went away in version 1.6 due to a misunderstanding of the proper way to include external DTDs. It was reintroduced to assist with validating parsers.

Added a description sub-element to the provenance element, so the provenance entry can contain more information about change justification documents and made provenance or provenanceRef acceptable sub-elements to variableDef and checkData elements at the request of Geoff Brian of DSTO.