internal DataColumn AddForeignKey(DataColumn parentKey)
{
Debug.Assert(parentKey != null, "AddForeignKey: Invalid paramter.. related primary key is null");
string keyName = XMLSchema.GenUniqueColumnName(parentKey.ColumnName, this);
DataColumn foreignKey = new DataColumn(keyName, parentKey.DataType, null, MappingType.Hidden);
Columns.Add(foreignKey);
return foreignKey;
}