On initialization, the Source object must create a Table object called VDATA and add it to its Tables collection. The Column objects in the table must match the VariableInstance objects in the MDM Document, if one is supplied. Otherwise, the Column objects must represent variables in the underlying data source.

If the underlying data source contains hierarchical (levels) data, VDATA can support a flattened form of the data at the lowest level, with higher-level data repeated for each lower-level case to which it applies. However, it may not always be possible to represent all of the variables this way; for example, if the data source has levels that are not in the same line of ancestry.