<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def views(self):
 """ Number of views this document has received on ProvStore """

        if self._views:
            return self._views
        elif not self.abstract:
            return self.read_meta()._views

        raise EmptyDocumentException()