code: def getInstalledOfferings(self):
          
          d = {}
          installed = self._siteStore.query(InstalledOffering)
          for installation in installed:
              offering = installation.getOffering()
              if offering is not None:
                  d[offering.name] = offering
          return d
docs: Return a mapping from the name of each L{InstalledOffering} in
          C{self._siteStore} to the corresponding L{IOffering} plugins.