From Just Solve the File Format Problem
DataDiagrammingML is an XML-based format which is one of the formats supported by Microsoft's Visio vector-graphic diagramming program starting in the 2003 version. This format is officially discontinued as of 2013.
The three varieties were:
- .VDX (XML Drawing)
- .VSX (XML Stencil)
- .VTX (XML Template)