synchronisation

Synchronisation is required in digital applications when updates may occur on several devices with copies of the same data which then need to be replicated across them all. For example, after you add an event to your phone calendar, you want the event to appear in your web and desktop apps as well. Most often this is achieved through a cloud service, which affectively acts as a 'golden copy' with each device syncing individually to this; device-to-device synchronisation occurs indirectly. Slightly more complicated algorithms are needed for direct device-to-device synchronisation, for example when they are connected via bluetooth, as there is no single clock and arbitor in the case of conflicts.

If there are several near sumultaneous updates on different devices, there is the potential for conflicts. Most often these will be on separate objects or distant parts of a dicuemnt, in which case both updates can be applied to get a combined version. The complications arise when there are multiple updates to the same object, or where there are constraints between several objects (for example, width and height of a graphical object with a fixed aspect ratio). Without care different devices and different users can end up with inconsistent 'copies' of the data, or cascade updates can lead to multiple copies of inserted data.