def _subArrayShape(self):
        """ Returns the shape of the sub-array
            An empty tuple is returned for regular fields, which have no sub array.
        """
        if self._h5Dataset.dtype.fields is None:
            return tuple() # regular field
        else:
            fieldName = self.nodeName
            fieldDtype = self._h5Dataset.dtype.fields[fieldName][0]
            return fieldDtype.shape
Returns the shape of the sub-array
            An empty tuple is returned for regular fields, which have no sub array.