This method must execute once..  Grab all schemas
        representing each targetNamespace.

def gatherNamespaces(self):
        '''This method must execute once..  Grab all schemas
        representing each targetNamespace.
        '''
        if self.usedNamespaces is not None:
            return

        self.logger.debug('gatherNamespaces')
        self.usedNamespaces = {}
            
        # Add all schemas defined in wsdl
        # to used namespace and to the Alias dict
        for schema in self._wsdl.types.values():
            tns = schema.getTargetNamespace()
            self.logger.debug('Register schema(%s) -- TNS(%s)'\
                %(_get_idstr(schema), tns),)
            if self.usedNamespaces.has_key(tns) is False:
                self.usedNamespaces[tns] = []
            self.usedNamespaces[tns].append(schema)
            NAD.add(tns)
            
        # Add all xsd:import schema instances
        # to used namespace and to the Alias dict
        for k,v in SchemaReader.namespaceToSchema.items():
            self.logger.debug('Register schema(%s) -- TNS(%s)'\
                %(_get_idstr(v), k),)
            if self.usedNamespaces.has_key(k) is False:
                self.usedNamespaces[k] = []
            self.usedNamespaces[k].append(v)
            NAD.add(k)