These days, I'm working on SyncML and Sync4J for Apogee synchronization purpose. I discovered some interesting points summed  up  in this article.

What is SyncML ?

SyncML is the specification of a synchronization protocol. Defined by the Open Mobile Alliance, it covers a large group of features. This protocol is mostly defined for connecting mobile devices like handhelds or mobile phones: thus it provides a lot of features oriented in this way. SyncML features includes:

• Several modes for synchronization
• Mobile device configuration and management

What happens during a synchronization ?

Basically, the synchronization is composed of three steps:

1. Exchange of device capabilities and authentication
2. Data exchange (client modifications first)
3. Data ids update

The third step might be strange. In fact SyncML defines two kinds of identifiers: the device local ones and the global ones. Then, when a new data is added on a client, it gets a local ID that needs to be "globalified".

What about authentication ?

SyncML defines a cred tag where to put the user id and password for the database. In this way a user can be logged on the database.

There is an other mecanism to allow some users to synchronize on some devices. This is contained in the SyncML header.

What about Sync4J ?

Sync4J is a free implementation of the SyncML standard. Provided by funambol it is composed of:

• a Data Synchronization Server to handle data synchronization
• a Device Management Server to configure the access and configuration of different devices
• an API for client applications in Java or C++
• an application for server configuration
• some database connectors

The server is an EJB and the messages are exchanged using HTTP, even if SyncML provides infos on other transport protocols. The authentication of the devices for synchronization is managed by a couple user/device called "Principals".

The Sync4J users are contained in a separate database. Even if I still didn't found it, it should be possible to replace it by a custom one... I hope. I didn't found any example about database authentication in the Sync4J demo set, by I imagine that it is implemented because it's defined in the specifications.