A playback apparatus for playing a digital stream in conjunction with an application the application being executed in the playback apparatus, the playback apparatus comprising: a package management unit (24,38) operable to generate package information by merging files recorded on a read-only recording medium and files on a rewritable recording medium, in accordance with merge management information recorded on the rewritable recording medium, the merge management information referencing files on the rewritable recording medium each of which is used for merging with the files recorded on the read-only recording medium; a selection unit (24,33) operable to detect a plurality of playable titles, each of which is a unit of playback, from the package information, and to select one of the detected titles as a current title; and a processing unit operable to execute an application which is executable within 2. the playback interval of the current title and which is specified in an object file associated with the current title; and a playback control engine (24,32) operable to control playback of a digital stream in accordance with playlist information that is specified in the object file associated with the current title and that is included in the package information, the playback apparatus characterized in that after the executed application requests the package management unit (24,38) to update the merge management information recorded on the rewritable recording medium, the package management unit (24,38) changes an attribute of the newly specified merge management information and an attribute of each file which is referenced from the newly specified merge management information and which is recorded on the rewritable recording medium to read-only before updating the package information, and at a point at which digital stream playback stops due to a current title change by the selection unit (24,33), the package management unit (24,38) generates new package information by merging files recorded on the read-only recording medium and files recorded on the rewritable recording medium, in accordance with the newly specified merge management information during an interval of the current title change. a package management unit (24,38) operable to generate package information by merging files recorded on a read-only recording medium and files on a rewritable recording medium, in accordance with merge management information recorded on the rewritable recording medium, the merge management information referencing files on the rewritable recording medium each of which is used for merging with the files recorded on the read-only recording medium; a selection unit (24,33) operable to detect a plurality of playable titles, each of which is a unit of playback, from the package information, and to select one of the detected titles as a current title; and a processing unit operable to execute an application which is executable within 2. the playback interval of the current title and which is specified in an object file associated with the current title; and a playback control engine (24,32) operable to control playback of a digital stream in accordance with playlist information that is specified in the object file associated with the current title and that is included in the package information, the playback apparatus characterized in that after the executed application requests the package management unit (24,38) to update the merge management information recorded on the rewritable recording medium, the package management unit (24,38) changes an attribute of the newly specified merge management information and an attribute of each file which is referenced from the newly specified merge management information and which is recorded on the rewritable recording medium to read-only before updating the package information, and at a point at which digital stream playback stops due to a current title change by the selection unit (24,33), the package management unit (24,38) generates new package information by merging files recorded on the read-only recording medium and files recorded on the rewritable recording medium, in accordance with the newly specified merge management information during an interval of the current title change.