Preface

This document is part of the LiveSupport project, Copyright Š 2004 Media Development Loan Fund, under the GNU GPL.

Author: $Author: fgerlits $
Version: $Revision: 1.4 $
Location: $Source: /home/cvs/livesupport/doc/model/Scheduler/index.html,v $

Scope

This document contains the specification of the LiveSupport Scheduler daemon.

This document contains embedded SVG figures, thus an SVG capable browser is needed to view it, or an SVG plugin like Adobe's SVG Viewer.

Requirements

Overview

The purpose of the LiveSupport Scheduler daemon is to execute playlists.

Goals

The scheduler daemon is a remotely accessible service accepting playlists on a local audio interface. Specific goals include:

remote manageability
handling remote audio clips referenced by playlists
low-latency playback

System functions

The main system functions are described below. There are three categories for these functions:

function category	meaning
evident	Should perform, and the user should be cognizant that it is performed
hidden	Should perform, but not visible to the users.
frill	Optional

ref#	function	category
F1.1	Accept uploaded playlists	evident
F1.2	Retrieve remote files referenced by playlists	hidden
F1.3	Access local files	hidden
F1.4	Provide status information	evident
F1.5	Log playlist execution for proof of broadcast reasons	evident
F1.6	Purge local file storage of unused audio clips	hidden
F1.7	Execute playlists	evident
F1.8	Play live streams as part of the playlist	hidden
F1.9	Remove playists from the schedule	evident
F1.10	Re-schedule playlsits	evident
F1.11	Delete playlists	evident
F1.12	Create playlists	evident
F1.13	Edit playlists	evident
F1.14	Start the scheduler daemon	evident
F1.15	Stop the scheduler daemon	evident

System attributes

Generic attributes

ref#	attribute	details and constraints	category
A1.1	operating system platform	Linux	must
A1.2	supported audio interfaces	ALSA (maybe also OSS?)	must
A1.3	supported playlist format	SMIL 2.0. only partial support is required, which focuses only on audio aspects of SMIL.	must
A1.4	supported audio clip formats	Ogg Vorbis, mp3, wav	must

Attributes related to system functions

ref#	function	ref#	attribute	details and constraints	category
F1.7	Execute playlists	A1.5	low latency	when executing playlists, very low latency should be achieved	must
		A1.6	handle time skew	the daemon has to take into account that the system's clock is not accurate. the clock is synchronized to an external regularly, but the resulting time-jump must be handled.	must
F1.8	Play live streams as part of the playlist	A1.7	supported audio stream formats	Ogg Vorbis via HTTP, mp3 via HTTP	must
F1.14 F1.15	Start / stop the scheduler daemon	A1.8	provide System V init style services	Provide a System V init interface to starting and stopping the scheduler daemon	must

Essential use cases

This section lists generic (essential) uses cases, that do not contain architecture-specific considerations.

UC-1 Upload playlist

ref#	UC-1
use case	Upload playlist
type	primary, essential
actors	Playlist editor
purpose	Upload a playlist
overview	The Playlist editor uploads a new playlist.
references	F1.1

Typical course of events

actor action		system response
1.	Playlist editor connects to the scheduler daemon with the intent of uploading a new playlist.
2.	The Playlist editor provides authentication information	3.	The system authenticates the Playlist editor and grants access.
4.	The Playlist editor presents the new playlist and the intended schedule for the playlist.	5.	The system validates the new playlist, and sees that it does not conflict with existing schedule.
		6.	The system stores the new playlist, adds it to the schedule, and sends confirmation to the Playlist editor.
7.	The Playlist editor receives confirmation and disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.
action 5: the system finds that the uploaded playlist is invalid, or it conflicts the existing schedule. the user is notified and the use case ends.

UC-2 Manage schedule

ref#	UC-2
use case	Manage schedule
type	primary, essential
actors	Playlist editor
purpose	View the schedule and remove or re-schedule playlists
overview	The Playlist editor reviews the schedule. If he decides to, he might remove or re-schedule some of these playlists.
references	F1.4, F1.9, F1.10

Typical course of events

actor action		system response
1.	Playlist editor connects to the scheduler daemon with the intent of viewing and editing the schedule.
2.	The Playlist editor provides authentication information	3.	The system authenticates the Playlist editor and grants access.
		4.	The system shows the Schedule to the Playlist editor
5.	The Playlist editor browses the Schedule, selects a playlist for detailed viewing.	6.	The system shows the details of the selected Playlist.
7.	The playlist editor removes a playlist from the schedule.	8.	The system removes the playlist from the schedule, than re-displays the updated schedle.
9.	The Playlist editor re-schedules a playlist	10.	The system removes the selected playlist from the schedule, and re-enters it at a new timepoint
11.	The Playlist editor browses the Schedule	12.	The system shows the Schedule to the playlist editor
13.	The Playlist editor disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.
action 8: the user tries to remove a non-existent playlist from the schedule. the user is notified, and the schedule is displayed to the user.
action 10: the new playtime for the schedule conflicts with already scheduled playlist playtimes. the user is notified, and the schedule is displayed again

UC-3 Manage playlists

ref#	UC-3
use case	Manage playlists
type	primary, essential
actors	Playlist editor
purpose	View and delete playlists
overview	The Playlist editor reviews the uploaded playlists. If he decides so, he might delete some of these playlists.
references	F1.4, F1.11

Typical course of events

actor action		system response
1.	Playlist editor connects to the scheduler daemon with the intent of viewing and deleting playlists.
2.	The Playlist editor provides authentication information	3.	The system authenticates the Playlist editor and grants access.
		4.	The system lists the available Playlists
5.	The Playlist editor browses the playlists, and selects one for detailed viewing.	6.	The system shows the details of the selected Playlist.
7.	The playlist editor deletes a playlist.	8.	The system deletes the playlist, than re-displays the list of available Playlists.
9.	The Playlist editor disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.
action 8: the user tries to delete a non-existent or a scheduled playlist. the user is notified, and the list of playlists is displayed to the user.

UC-4 Retrieve remote files

ref#	UC-4
use case	Retrieve remote files
type	primary, essential
actors	(internal actor, initiator), Media archive, Local storage
purpose	Retrieve remote files referenced by active playlists and store them in the local storage
overview	The daemon contacts the remote media archive and retrieves audio clips referenced by active playlists. The clips are stored locally for playing.
references	F1.2

Note that this use case is somewhat reversed, as it is initiated by the system (not an actor), and the main tasks are done by an external actor (the Media archive).

Typical course of events

actor action		system response
1.	An Internal actor triggers the retrieval of some remote files.	2.	The system looks up the URN of the remote file, and determines the Media archive to contact regarding the file.
		3.	The system contacts the Local storage and sends authorization information
4.	Local storage authenticates the system and grants access	5.	The system iniquires the local storage about the availability of the file to download in the Local storage by presenting its unique ID
6.	Local storage tells if the required file is already stored or not.	7.	If the file is available in the local storage, the use case ends. Otherwise, it continues.
		8.	The system contacts the Media archive and sends authorization information
9.	Media archive authenticates the system and grants access	10.	The system requests an audio clip by presenting its unique ID
11.	Media archive looks up the file, and presents it to the system	12.	The system retrieves the file and closes the connection to the Media archive
		13.	The system presents the file to Local storage
14.	Local storage stores the file under the specified unique ID	15.	The system closes the connection to Local storage.

Alternate courses

action 4: the Local storage finds that the system can not be authenticated. the system is notified and the use case ends.
action 9: the Media archive finds that the system can not be authenticated. the system is notified and the use case ends.
action 11: the Media archive does not hold the requested audio clip. the system is notified and the use case ends.

UC-5 Review play log

ref#	UC-5
use case	Review play log
type	secondary, essential
actors	Broadcast auditor
purpose	Review what has been played
overview	The Broadcast auditor reviews the audio clips that have been played in a selected time interval. He may generate reports for proof of broadcast reasons.
references	F1.4

Typical course of events

actor action		system response
1.	Broadcast auditor connects to the scheduler daemon with the intent of reviewing what has been played.
2.	The Broadcast auditor provides authentication information	3.	The system authenticates the Broadcast auditor and grants access.
3.	The Broadcast auditor browses through the play log in a time-ordered manner.	4.	The system displays the play log entries.
5.	The Broadcast auditor requests a play report for a given time period.	6.	The system displays the requested report.
7.	The Broadcast auditor disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.

UC-6 Create playlist

ref#	UC-6
use case	Create playlist
type	secondary, essential
actors	Playlist editor
purpose	Create a new playlist, and then edit it.
overview	The Playlist editor connects to the Scheduler with the aim of creating a new playlist. A basic user interface is provided, which allows professionals to create and edit the playlsits on the system.
references	F1.12, F1.13

Typical course of events

actor action		system response
1.	Playlist editor connects to the scheduler with the intent of creating a new playlist.
2.	The Playlist editor provides authentication information	3.	The system authenticates the Playlist editor and grants access.
4.	The Playlist editor signals that he whishes for a new playlist	5.	The system creates a new, empty playlist, and opens it for editing.
6.	The Playlist editor edits the new playlist. See UC-7 actions 7-15 for details.
7.	The Playlist editor disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.

UC-7 Edit playlist

ref#	UC-7
use case	Edit playlist
type	secondary, essential
actors	Playlist editor
purpose	Edit a previoulsy uploaded playlist
overview	The Playlist editor connects to the Scheduler with the aim of either editing an existing playlist. A basic user interface is provided, which allows professionals to edit the playlsits on the system.
references	F1.12

Typical course of events

actor action		system response
1.	Playlist editor connects to the scheduler with the intent of editing a playlist.
2.	The Playlist editor provides authentication information	3.	The system authenticates the Playlist editor and grants access.
		4.	The system lists the available playlists.
5.	The Playlist editor selects a playlist for editing.	6.	The system opens the playlist in editing mode.
7.	The Playlist editor browses the available Audio clips	8.	The system shows the list of available audio clips
9.	The Playlist editor selects an Audio clip	10.	The system displays details on the audio clip.
11.	The Playlist editor ads a new audio clip to the playlist, at a certain timepoint in the playlist.	12.	The new audio clip is added to the playlist.
13.	The Playlist editor removes an audio clip from the playlist.	14.	The audio clip is removed from the playlist.
15.	The Playlist editor edits the fade-in or fade-out of a clip in the playlist.	16.	The fade-in or fade-out is edited.
17.	The Playlist editor saves the playlist.	18.	The playlist is validated.
		19.	The playlist is saved.
20.	The Playlist editor disconnects.

Alternate courses

action 3: the system finds that the user can not be authenticated. the user is notified and the use case ends.
action 6: the selected playlist is currently being executed. the user is notified that executing playlists can not be edited and the use case ends.
action 17: the user decides not to save the playlist, but to revert to the version prior to editing. the playlist is reverted, and is shown to the user in non-edit mode.
action 18: the playlist turns out not be valid. the user is notified that such a playlist can not be saved, and is given an opportunity to further edit the playlist. validation errors are also shown.

UC-8 Start/stop scheduler

ref#	UC-8
use case	Start/stop scheduler
type	primary, essential
actors	Administrator
purpose	Start and stop the scheduler daemon
overview	The adminisitrator starts the scheduler deamon by invoking a System V init-style startup script. He may also stop the deamon with the same script.
references	F1.14, F1.15, A1.8

Typical course of events

actor action		system response
1.	The Administrator invokes the scheduler's System V init script with the start parameter
		2.	The scheduler daemon starts up.
3.	The Administrator checks to see if the scheduler daemon is running	4.	The scheduler daemon reports that it is running.
5.	The Administrator stops the scheduler deamon.	6.	The scheduler daemon stops.

Alternate courses

action 2: if the scheduler is already running, indicate the starting attempt as an error.
action 4: if the scheduler daemon is not running, it is reported that it is not running.
action 6: if the scheduler daemon is not running, it is not stopped.

Conceptual model

The following figure displays the semantic concepts identified for the Scheduler daemon, and the main associations between the concepts.

Concepts

concept	description
Media archive	An archive external to the system, which holds Audio clips. The archive offers its clips for download by requesting clips based on their unique ids.
Clip retriever	Retrieves Audio clips from the Media archive and stores them in local storage.
Local storage	A local store of Audio clips. Provides access to each clip based on the clips' unique id. Allows random access to the clip files.
Audio clip	A uniquely identified audio file.
Playlist	A metafile, containing references to Audio clips, and information on how the clips should be played.
PlaylistElement	An association class describing the specifics of an instance of an Audio clip in a playlist.
FadeInfo	A class describing fade in or fade out characteristics for an Audio clip in a Playlist
Playlist store	A container holding a range of playlists.
Schedule	Contains Schedule entries
Schedule entry	Contains the time and details of when a playlist should be played.
Scheduler daemon	Executes playlists at timepoints specified by the schedule.
Play log	A logging facility, holding Play log entries.
Play log entry	A record of when an Audio clip was played.
Play report	An audit report of what Audio clips have been played in a certain time period
Authentication	Provides authentication services
Playlist editor	An external editor, managing playlists.
Broadcast auditor	An external auditor, browsing the Play log.
Administrator	The administrator responsible for starting and stopping the scheduler daemon.

Associations

source	association	target	description
Clip retriever	Retrieves clips from	Media archive
Media archive	Contains	Audio clip
Clip retriever	Stores clips in	Local storage
Local storage	Contains	Audio clip
Playlist	References by PlaylistElement	Audio clip
PlaylistElement	Fades in with	FadeInfo
PlaylistElement	Fades out with	FadeInfo
Playlist store	Contains	Play list
Playlist editor	Uploads playlist to	Playlist store
Playlist editor	Manages schedule in	Schedule	The Playlist editor schedules playlists.
Schedule	Contains	Schedule entry
Schedule entry	References	Playlist
Scheduler daemon	Executes	Schedule	The Scheduler daemon plays the scheduled playlists.
Scheduler daemon	Logs into	Play log	The Scheduler daemon logs all the played audio clips into the Play log for proof of broadcast purposes.
Play log	Contains	Play log entry
Play log	Generated	Play report	The play log generates reports based on Play log entries.
Play log entry	References	Audio clip
Broadcast auditor	Browses entries from	Play log
Broadcast auditor	Requests	Play report
Playlist editor	Is authenticated by	Authentication
Broadcast auditor	Is authenticated by	Authentication
Administrator	Manages	Scheduler daemon

System behavior

The behavior of the system as a whole as experienced from the outside is discussed in this section.

System sequence diagrams

System diagrams are presented for each use case below.

UC-1 Upload playlists

UC-2 Manage schedule

UC-3 Manage playlists

UC-4 Retrieve remote files

UC-5 Review play log

UC-6 Create playlist

UC-7 Edit playlist

UC-8 Start/stop scheduler

System objects

The following figures shows the system objects and their functions, as derived from the system sequence diagrams.

Contracts

For all operations exposed in the system sequence diagrams, the following contracts are defined.

Contract for Scheduler : authenticate

See Authentication : authenticate

Contract for Scheduler : uploadPlaylist

Name	uploadPlaylist (playlist : Playlist, playtime: Schedule) : UniqueId
Responsibilities	Upload a playlist and put it into the schedule.
Type	system
Cross-reference	F1.1, UC-1
Notes
Exceptions	If the uploaded playlist is not valid, indicate as an error If the proposed schedule conflicts with existing schedules, indicate as an error
Output	the unique id of the ScheduleEntry created with this upload
Pre-conditions	none
Post-conditions	condition	type
	A new Playlist is created, storing the uploaded playlist	instance creation
	Playlist is entered into the Playlist store	association formed
	A new Schedule is created, according to the supplied schedule	instance creation
	Schedule is associated with the Playlist	association formed

Contract for Scheduler : displaySchedule

Name	displaySchedule (from : TimeStamp, to : TimeStamp) : Schedule
Responsibilities	Display Schedule entries for a time period.
Type	system
Cross-reference	F1.4, UC-2
Notes
Exceptions	none
Output	The Schedule entries for the specified time period.
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : displayPlaylist

Name	displayPlaylist (playlistId : UniqueId) : Playlist
Responsibilities	Display a specific playlist
Type	system
Cross-reference	F1.4, UC-3
Notes
Exceptions	If no playlist exists for the specified playlistId, indicate as an error.
Output	The requested playlist.
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : deletePlaylist

Name	deletePlaylist (playlist : Playlist) : void
Responsibilities	Delete a specific playlist
Type	system
Cross-reference	F1.11, UC-3
Notes
Exceptions	If no playlist exists for the specified playlistId, indicate as an error. If the playlist is referenced by any Schedule entry, indicate as an error.
Output	none
Pre-conditions	none
Post-conditions	condition	type
	The playlist is removed from the Playlist store.	association broken
	References by the playlist to Audio clips removed	association broken
	The playlist is deleted	instance deletion

Contract for Scheduler : removeFromSchedule

Name	removeFromSchedule (scheduleEntryId : UniqueId) : bool
Responsibilities	Remove a specific playlist from a schedule entry
Type	system
Cross-reference	F1.9, UC-2
Notes
Exceptions	If no ScheduleEntry by the specified scheduleEntryId exist, indicate as an error.
Output	true if the specified entry was removed, false if it did not exist.
Pre-conditions	none
Post-conditions	condition	type
	Reference to the playlist by the scheduleEntry is removed.	association broken
	The ScheduleEntry specified by the scheduleEntryId is deleted	instance deletion

Contract for Scheduler : reschedule

Name	reschedule (scheduleEntryId : UniqueId, playtime : TimeStamp) : bool
Responsibilities	Change when a certain playlist is scheduled to play.
Type	system
Cross-reference	F1.10, UC-2
Notes
Exceptions	If no ScheduleEntry by the specified scheduleEntryId exist, indicate as an error. If the new playtime conflicts with other schedule entries, indicate as an error.
Output	false on errors
Pre-conditions	none
Post-conditions	condition	type
	The time attribute of scheduleEntry is updated to the supplied playtime.	attribute modification

Contract for Scheduler : displayPlaylists

Name	displayPlaylists () : Playlist
Responsibilities	Display Playlists contained in the Playlist store
Type	system
Cross-reference	F1.4, UC-3
Notes
Exceptions	none
Output	The playlists contained in the Playlist store.
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : displayPlayLog

Name	displayPlayLog () : Play log
Responsibilities	Display Play log entries contained in the Play log
Type	system
Cross-reference	F1.4, UC-5
Notes
Exceptions	none
Output	The play log entries contained in the Play log.
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : generatePlayReport

Name	generatePlayReport (from : TimeStamp, to : TimeStamp) : Play report
Responsibilities	Present a report on what Audio clips have been played to the Broadcast auditor.
Type	system
Cross-reference	F1.4, UC-5
Notes
Exceptions	none
Output	A report on the played Audio clips played in the specified time period.
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : createPlaylist

Name	createPlaylist () : Playlist
Responsibilities	Create a new playlist
Type	system
Cross-reference	F1.12, UC-6
Notes	A new playlist is created, and is immediately locked for editing.
Exceptions	none
Output	none
Pre-conditions	none
Post-conditions	condition	type
	A new Playlist is created	instance creation
	The lockedForEditing attribute is set to true for the playlist	attribute modification
	The playlist is added to the Playlist store	association formed

Contract for Scheduler : openPlaylistForEditing

Name	openPlaylistForEditing (playlist : Playlist) : void
Responsibilities	Open a playlist for editing
Type	system
Cross-reference	F1.13, UC-7
Notes	A playlist is opened for editing. The playlist may not be played when being edited. Also, active (currently executing) playlists may not be opened for editing. This is in effect a lock, which is released by saving the playlist.
Exceptions	if the playlist is currently being executed, indicate as an error.
Output	none
Pre-conditions	none
Post-conditions	condition	type
	The current version of the playlist is stored, in case the user wants to revert to the last saved version (see revertEditedPlaylist)	instance creation
	The lockedForEditing attribute is set to true for the playlist	attribute modification

Contract for Scheduler : addAudioClipToPlaylist

Name	addAutioClipToPlaylist (playlist : Playlist, audioClip : AudioClip, relativeOffset : Time) : void
Responsibilities	Add an Audio clip to a Playlist
Type	system
Cross-reference	F1.13, UC-7
Notes	The Audio clip is added to the playlist with the specified relativeOffset from the beginning of the Playlist.
Exceptions	none
Output	none
Pre-conditions	the Playlist is currently opened for editing
Post-conditions	condition	type
	The new PlaylistElement is created associating the playlist with the audio clip, with the specified relativeOffset	association formed, instnace creation

Contract for Scheduler : displayAudioClips

Name	displayAudioClips () : AudioClip
Responsibilities	Display the audio clips known to the Scheduler
Type	system
Cross-reference	F1.13, UC-7
Notes	none
Exceptions	none
Output	The Audio clips kown to the Scheduler
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : displayAudioClip

Name	displayAudioClip (audioClipId : UniqueId) : AudioClip
Responsibilities	Display the audio clip specified by the audioClipId
Type	system
Cross-reference	F1.13, UC-7
Notes	none
Exceptions	if no audio clip by the specified id exists, indicate as an error
Output	The Audio clip specified by the audioClipId
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : removeAudioClipFromPlaylist

Name	removeAutioClipFromPlaylist (playlist : Playlist, relativeOffset: Time) : void
Responsibilities	Remove an Audio clip at the given relative offset from a Playlist
Type	system
Cross-reference	F1.13, UC-7
Notes	The Audio clip is removed from the Playlist.
Exceptions	If there is no Audio clip at the specified relative offset in the playlist, indicate as an error.
Output	none
Pre-conditions	the Playlist is currently opened for editing
Post-conditions	condition	type
	The PlaylistElement associating the AudioClip with the Playlist is removed, with the related FadeInfo instances	instance deletion, association broken

Contract for Scheduler : updateFadeInFadeOut

Name	updateFadeInFadeOut (audioClip : AudioClip, playlist : Playlist) : void
Responsibilities	Update the fade-in and fade-out parameters for an audio clip playing in a playlist.
Type	system
Cross-reference	F1.13, UC-7
Notes	none
Exceptions	If the Audio clip is not in the playlist, indicate as an error.
Output	none
Pre-conditions	the Playlist is currently opened for editing
Post-conditions	condition	type
	The fade-in and fade-out parameters for the audio clip in the playlist are updated	attribute modification

Contract for Scheduler : validatePlaylist

Name	validatePlaylist (playlist : Playlist) : boolean
Responsibilities	Validate a playlist for being complete.
Type	system
Cross-reference	F1.13, UC-7
Notes	The playlist is checked for being complete (not containing silence) and other sanity criteria.
Exceptions	none
Output	none
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : savePlaylist

Name	savePlaylist (playlist : Playlist) : void
Responsibilities	The playlist is saved.
Type	system
Cross-reference	F1.13, UC-7
Notes	none
Exceptions	If the playlist is not valid, indicate as an error.
Output	none
Pre-conditions	the Playlist is currently opened for editing
Post-conditions	condition	type
	The lockedForEditing attriubute is set to false for the playlist	attribute modification
	The old version of the Playlist that could have been used for reverting is deleted (see revertEditedPlaylist)	instance deletion

Contract for Scheduler : revertEditedPlaylist

Name	revertEditedPlaylist (playlist : Playlist) : void
Responsibilities	Changes are discarded for a Playlist that is being edited.
Type	system
Cross-reference	F1.13, UC-7
Notes	The contents of the playlist are reverted to the state prior to when editing began on it.
Exceptions	none
Output	none
Pre-conditions	the Playlist is currently opened for editing
Post-conditions	condition	type
	The contents of the Playlist are reverted to the last saved version. This includes deleting all created PlaylistElement and FadeInfo instances.	attribute modification, instance deletion
	The lockedForEditing attriubute is set to false for the playlist	attribute modification

Contract for Scheduler : start

Name	start () : void
Responsibilities	Starts the scheduler daemon
Type	system
Cross-reference	F1.14, UC-8
Notes	A System V init-style daemon starting entry point
Exceptions	none
Output	none
Pre-conditions	The scheduler daemon is currently not running
Post-conditions	condition	type
	The scheduler daemon object is created	instance creation
	All the necessary structures are created for the deamon to run	instance creation

Contract for Scheduler : isRunning

Name	isRunning () : boolean
Responsibilities	Tells if the scheduler daemon is running
Type	system
Cross-reference	UC-8
Notes	A System V init-style daemon status entry point
Exceptions	none
Output	true of the daemon is running, false otherwise
Pre-conditions	none
Post-conditions	none

Contract for Scheduler : stop

Name	stop () : void
Responsibilities	Stops the scheduler daemon
Type	system
Cross-reference	F1.15, UC-8
Notes	A System V init-style daemon stopping entry point
Exceptions	none
Output	none
Pre-conditions	The scheduler daemon is currently running
Post-conditions	condition	type
	The scheduler daemon object is deleted	instance deletion

Contract for Media archive : authenticate

TODO: move to Media archive spec

Name	authenticate (authenticationInfo : AuthenticationInfo) : boolean
Responsibilities	Check if the provided authentication info is recognized.
Type	interface
Cross-reference	UC-4
Notes
Exceptions	none
Output	true if the provided authentication is recognized, false otherwise
Pre-conditions	none
Post-conditions	none

Contract for Media archive : retrieveAudioClip

TODO: move to Media archive spec

Name	retrieveAudioClip (clipId : UniqueId) : AudioClip
Responsibilities	Retrieve an AudioClip specified by the supplied audio clip id.
Type	interface
Cross-reference	F1.2, UC-4
Notes
Exceptions	if no audio clip exists with the supplied id, indicate as an error
Output	the requested audio clip
Pre-conditions	none
Post-conditions	condition	type
	A new Audio clip is created and filled with the contents of the retrieved audio clip	instance creation
	Audio clip is entered into Local storage	association formed

Contract for Local storage : authenticate

TODO: move to Local storage spec

Name	authenticate (authenticationInfo : AuthenticationInfo) : boolean
Responsibilities	Check if the provided authentication info is recognized.
Type	interface
Cross-reference	UC-4
Notes
Exceptions	none
Output	true if the provided authentication is recognized, false otherwise
Pre-conditions	none
Post-conditions	none

Contract for Local storage : existsAudioClip

TODO: move to Local storage spec

Name	existsAudioClip (audioClipId : UniqueId) : boolean
Responsibilities	Tell if an audio clip by the provided unique id is stored in the Local storage
Type	interface
Cross-reference	UC-4
Notes
Exceptions	none
Output	true if an audio clip with the provided id exists, false otherwise
Pre-conditions	none
Post-conditions	none

Contract for Local storage : storeAudioClip

TODO: move to Local storage spec

Name	storeAudioClip (audioClip : AudioClip) : void
Responsibilities	Store an audio clip.
Type	interface
Cross-reference	UC-4
Notes
Exceptions	none
Output	none
Pre-conditions	none
Post-conditions	The supplied audio clip is stored in the storage.

Glossary

playlist
The playlist is a metafile, containing references to audio clips that should be played, and details on how they should be played.