This document provides the Operation Contracts for the Tanager project. Operation Contracts will be generated from the System Sequence Diagrams and show the public interface for the Tanager system. The Operation Contracts will show the relationship between calls made on the public interface and changes made in the Domain Model.

1.2. Scope

This document describes the Operation Contracts for the Tanager project.

1.3. Definitions, Acronyms, and Abbreviations

A complete list of definitions, acronyms, and abbreviations can be found in the Tanager Glossary.

1.1. Diagrams

All diagrams in this document were generated using Gentleware’s Poseidon for UML tool.

1.2. References

Larman, Craig. 2005. Applying UML and Patterns. Westford, MA: Prentice Hall. 09 August, 2005 <http://www.phptr.com/title/0131489062>.

Poseidon for UML. 2005. Gentleware AG. 20 January, 2007 <http://www.gentleware.com/uml-software-pe.html>.

Tanager Domain Model. 2006. Bob Lavey. 20 January, 2007 <TanagerSystemSequenceDiagramSpecification.htm>.

Tanager System Sequence Diagram Specification. 2007. Bob Lavey. 25 January, 2007 <TanagerSystemSequenceDiagramSpecification.htm>.

Tanager Use Case Specification. 2007. Bob Lavey. 19 January, 2007 <TanagerUseCaseModel.htm>.

1.3. Overview

This document will provide a more detailed view of the public interface to the Tanager system. It will describe how the users will use the system, and how they expect the system to behave.

2. Externally-Visible State Diagram

2.1. Application State Diagram

2.2. UI State Diagram

3. Operation Contracts

3.1. DeleteSong

Operation	DeleteSong(uuid: UUID)
Cross References	Use Cases: Delete A Song
Preconditions	None
Postconditions	· The Song instance, song, with the given UUID was removed from the current playlist · The Song instance, song, with the given UUID was destroyed

3.2. DownloadSong

Operation	DownloadSong(filename: String)
Cross References	Use Cases: Download A Song
Preconditions	None
Postconditions	· A new Song instance, song, was created with the given filename and the current date, and it was associated with the Playlist instance · The new Song instance was written to the FileStore

3.3. GetPlaylist

Operation	GetPlaylist(): PlaylistView
Cross References	Use Cases: View Playlist, Delete a Song
Preconditions	None
Postconditions	· A new PlaylistView instance, playlistView was created · The new PlaylistView instance was returned to the called

3.4. GetPlaylistTypes

Operation	GetPlaylistTypes(): PlaylistTypeList
Cross References	Use Cases: Select Playlist
Preconditions	None
Postconditions	· A new PlaylistTypeList instance, playlistTypeList was created · The new PlaylistTypeList was populated with all the available playlist types · The new PlaylistTypeList instance was returned to the called

3.5. GetVolume

Operation	GetVolume(): int
Cross References	Use Cases: Volume Adjustments
Preconditions	None
Postconditions	· The current volume was returned to the caller

3.6. Pause

Operation	Pause()
Cross References	Use Cases: Pause Music
Preconditions	systemState.state is Playing
Postconditions	· systemState.state was changed to Paused · The song that was playing and the point at which it was paused were saved to the SystemState instance · The song that was playing has stopped · The SystemState instance, systemState was saved to non-volatile storage

3.7. Play

Operation	Play()
Cross References	Use Cases: Play Music
Preconditions	systemState.state is Paused or Idle
Postconditions	· systemState.state was changed to Playing · If the system was in the Paused state, the paused song has resumed playing from the point at which it had been paused. · If the system was in the Idle state, the first song from the playlist has begun playing · The SystemState instance, systemState was saved to non-volatile storage

3.8. PowerOff

Operation	PowerOff()
Cross References	Use Cases: Power Off
Preconditions	The system was previously powered on.
Postconditions	· The SystemState instance, systemState was saved to non-volatile storage · The SongCollection instance, songCollection, was saved to non-volatile storage · The system replied that it was ready to exit

3.9. PowerOn

Operation	PowerOn()
Cross References	Use Cases: Power On
Preconditions	None
Postconditions	· A MusicPlayer instance, musicPlayer, was created · A SystemState instance, systemState was created and was associated with the MusicPlayer instance · A Playlist instance, playlist, was created and was associated with the MusicPlayer instance · A SongCollection instance, songCollection, was created and was associated with the Playlist instance · A Song instance was created for each file found in the FileStore, and each Song instance was associated with the SongCollection instance

3.10. RestartSong

Operation	RestartSong()
Cross References	Use Cases: Restart Current Song
Preconditions	systemState.state is Playing
Postconditions	· The song that was playing was restarted from the beginning

3.11. SelectPlaylistType

Operation	SelectPlaylistType(PlaylistTypeEnum: playlistType)
Cross References	Use Cases: SelectPlaylistType
Preconditions	systemState.state is Idle
Postconditions	· The new playlist type was used to reorder the collection of downloaded songs · The new playlist type was saved to non-volatile storage

3.12. SetVolume

Operation	SetVolume(volume: int)
Cross References	Use Cases: Volume Adjustments
Preconditions	None
Postconditions	· If the systemState was Playing or Paused, the new volume setting was given to the playing or paused song · The new volume setting was saved to non-volatile storage

3.13. SkipToPreviousSong

Operation	SkipToPreviousSong()
Cross References	Use Cases: Skip To Previous Song
Preconditions	systemState.state is Playing
Postconditions	· The song that was playing was stopped · If the song that was playing was the first song in the playlist, it was restarted · If the song that was playing was not the first song in the playlist, the previous song in the playlist was started

3.14. Stop

Operation	Stop()
Cross References	Use Cases: Stop Music
Preconditions	systemState.state is Playing or Paused.
Postconditions	· If the systemState was Playing, the song that was playing has stopped · systemState.state was changed to Idle · The SystemState instance, systemState was saved to non-volatile storage

4. Revision History

Date	Version	Description	Author
06 Feb, 2006	1.0 – Elaboration Phase 1	Initial Revision. Added operation contracts for operations discovered in Power On and Download A Song main success scenarios.	Bob Lavey
14 Sep, 2006	1.1 – Elaboration Phase 1	Added operation contract for operations discovered in Power Off main success scenario.	Bob Lavey
22 Oct, 2006	1.2 – Elaboration Phase 1	Revised with comments from Dr. Leavens’ review.	Bob Lavey
24 Oct, 2006	1.3 – Elaboration Phase 1	Modified operation contracts for operations in Download a Song main success scenario.	Bob Lavey
11 Nov, 2006	2.0 – Elaboration Phase 2	Reordered operations to put them in alphabetical order. Added operations discovered in Play Music and Pause Music scenarios.	Bob Lavey
11 Dec, 2006	3.0 – Elaboration Phase 3	Added operations discovered in Stop Music scenario.	Bob Lavey
30 Dec, 2006	3.1 – Elaboration Phase 3	Added operations discovered in Enter Menus and Exit Menus scenarios.	Bob Lavey
13 Jan, 2007	3.2 – Elaboration Phase 3	Added operations discovered in View Playlist and Delete a Song scenarios.	Bob Lavey
15 Jan, 2007	3.3 – Elaboration Phase 3	Added operations discovered in Volume Adjustments scenarios.	Bob Lavey
15 Jan, 2007	3.4 – Elaboration Phase 3	Added externally-visible state machine.	Bob Lavey
19 Jan, 2007	3.5 – Elaboration Phase 3	Updated based on Dr. Leavens’ review. Removed all discussion of menus, since that is a UI concept.	Bob Lavey
16 Jan, 2007	4.0 – Elaboration Phase 4	Added operations discovered in Select Playlist Type scenario.	Bob Lavey
20 Jan, 2007	4.1 – Elaboration Phase 4	Added operations discovered in Restart Current Song scenario.	Bob Lavey
25 Jan, 2007	4.2 – Elaboration Phase 4	Added operations discovered in Skip to Previous Song scenario. Updated Application State Machine, and added UI State Machine.	Bob Lavey