def do_schema(self, line):
        """
        schema

        schema --clear

        schema filed_name field_type
        """
        args = self.getargs(line)

        if not args:
            for k in sorted(self.schema):
                print "%s\t%s" % (k, self.schema[k])
        elif args[0] == "--clear":
            self.schema.clear()
        else:
            fname = args[0]
            ftype = args[1]

            if not ftype in VALID_TYPES:
                print "invalid type: use %s" % list(VALID_TYPES)
            else:
                self.schema[fname] = ftype