[dtp-dev] Design Proposal - Work Offline Mode

[rcernich@xxxxxxxxxx]

Hey all,

I'm looking at adding hooks within the framework to support an offline
mode.  The following describes the user interaction as well as some details
regarding API.  Please let me know if this is adequate or if you have any
suggestions as to how this should work, what API should be involved, etc.

Actions/commands:  The following describes the actions, their enablement
and behavior, required for offline support.

Connect:
   connection state == disconnected
      enablement:  enabled.
      behavior:  An attempt to connect to the server is made.  If the
      connection attempt was successful, the connection profile is moved to
      a "connected" state.  This does not differ from the current connect
      action behavior.
   connection state == connected
      enablement: disabled.
      behavior: none.
   connection state == offline
      enablement: enabled.
      behavior: An attempt to connect to the server is made.  If the
      attempt is successful, the tree is updated to reflect the state of
      the server.  The provider is responsible for synchronizing the
      offline model with the connected model (e.g. propagating offline
      changes onto the server).  While no support (including API hooks) for
      performing this task is provided by the framework, the provider will
      be able to determine that the connection state is changing from
      "offline" to "connected."  If the connection attempt is successful,
      the connection profile is moved to a "connected" state.

Disconnect:
   connection state == disconnected
      enablement:  disabled.
      behavior:  none.
   connection state == connected
      enablement: enabled.
      behavior: Disconnects from the server.  The connection profile is
      moved to a "disconnected" state.
   connection state == offline
      enablement: enabled.
      behavior: The connection profile is moved to a "disconnected" state.
      The provider must determine whether or not it is appropriate to
      persist any modifications made to the offline model.

Work offline:
   connection state == disconnected
      enablement:  enabled.
      behavior:  If a persisted "snapshot" of the server's state exists, it
      is loaded and presented to the user and the state of the connection
      profile is moved to "offline."  If a persisted snapshot does not
      exist or cannot be loaded, the state of the connection profile
      remains unchanged.
   connection state == connected
      enablement: enabled.
      behavior: A snapshot of the server's state is persisted prior to
      disconnecting from the server.  If the persistence operation was
      successful, the connection to the server is closed the connection
      profile is moved to an "offline" state.  If there was a problem
      persisting the state, the connection to the server will remain open
      and the connection profile's state will remain unchanged.
   connection state == offline
      enablement: disabled.
      behavior: none.

Save offline:
   connection state == disconnected
      enablement:  disabled.
      behavior:  none.
   connection state == connected
      enablement: enabled.
      behavior: A snapshot of the server's state is persisted.  The
      connection profile's connected state remains unchanged.
   connection state == offline
      enablement: enabled.
      behavior: The persisted snapshot of the server's state is updated.
      The connection profile's connected state remains unchanged.

API Modifications:
IOfflineConnectionFactory - an extended version of IConnectionFactory that
provides hooks for integrating with offline actions.
IOfflineConnection - an extended version of IConnection that provides hooks
for integrating with offline actions.

Sequence diagrams: (or the best approximation in text form)
Connect action:
   connected state == disconnected
      IOfflineConnectionFactory.createConnection(IConnectionProfile)-->returns
 new IOfflineConnection
   connected state == connected
      no action
   connected state == offline
      IOfflineConnection.attach()

Disconnect action:
   connected state == disconnected
      no action
   connected state == connected
      IOfflineConnection.close()
   connected state == offline
      IOfflineConnection.close()

Work offline action:
   connected state == disconnected
      IOfflineConnection.createOfflineConnection()-->returns new
      IOfflineConnection
   connected state == connected
      IOfflineConnection.detach()
   connected state == offline
      no action

Save offline action:
   connected state == disconnected
      no action
   connected state == connected
      IOfflineConnection.save()
   connected state == offline
      IOfflineConnection.save()

Please let me know if you have any questions, comments, concerns, etc.

Best regards,
Rob Cernich
DTP Connectivity Project Lead