def build(self, builder):
        """Build XML by appending to builder"""
        params = dict(OID=self.oid)
        params["mdsol:ProjectType"] = self.project_type

        builder.start("Study", params)

        # Ask children
        if self.global_variables is not None:
            self.global_variables.build(builder)

        if self.basic_definitions is not None:
            self.basic_definitions.build(builder)

        if self.metadata_version is not None:
            self.metadata_version.build(builder)

        builder.end("Study")