Emits the background knowledge in prolog form for Aleph.

def background_knowledge(self):
        '''
        Emits the background knowledge in prolog form for Aleph.
        '''
        modeslist, getters = [self.mode(self.__target_predicate(), [('+', self.db.target_table)], head=True)], []
        determinations, types = [], []
        for (table, ref_table) in self.db.connected.keys():
            if ref_table == self.db.target_table:
                continue  # Skip backward connections
            modeslist.append(
                self.mode('%s_has_%s' % (table.lower(), ref_table), [('+', table), ('-', ref_table)], recall='*'))
            determinations.append(
                ':- determination(%s/1, %s_has_%s/2).' % (self.__target_predicate(), table.lower(), ref_table))
            types.extend(self.concept_type_def(table))
            types.extend(self.concept_type_def(ref_table))
            getters.extend(self.connecting_clause(table, ref_table))
        for table, atts in self.db.cols.items():
            for att in atts:
                if att == self.db.target_att and table == self.db.target_table or \
                                att in self.db.fkeys[table] or att == self.db.pkeys[table]:
                    continue
                modeslist.append(self.mode('%s_%s' % (table, att), [('+', table), ('#', att.lower())], recall='*'))
                determinations.append(':- determination(%s/1, %s_%s/2).' % (self.__target_predicate(), table, att))
                types.extend(self.constant_type_def(table, att))
                getters.extend(self.attribute_clause(table, att))
        return '\n'.join(self.user_settings() + modeslist + determinations + types + getters + self.dump_tables())