We define two collection:
        - Number of work injuries ("Arbetsolycka")
        - Number of workrelated diseases ("Arbetssjukdom")
        Each contains four datasets:
        - Per municipality and year
        - Per county and year
        - Per municipality and month
        - Per municipality and year

def _fetch_itemslist(self, item):
        """ We define two collection:
        - Number of work injuries ("Arbetsolycka")
        - Number of workrelated diseases ("Arbetssjukdom")
        Each contains four datasets:
        - Per municipality and year
        - Per county and year
        - Per municipality and month
        - Per municipality and year
        """
        if item.is_root:
            for c in ["Arbetsolycka", "Arbetssjukdom"]:
                yield Collection(c, blob=(c, None, None))
        else:
            c = item.id
            for r in [u"kommun", u"län"]:
                for p in [u"år", u"månad"]:
                    yield Dataset(u"%s-%s-%s" % (c, r, p),
                                  blob=(c, r, p),
                                  label=u"%s, antal per %s och %s" % (c, r, p))