Database synchronization between online and offline website

I am looking for someone to install and do the following configuration to osclass script: 1. I want it to be available online and offline. The website would allow people to normally interact with the application, inserting, editing and deleting ads as they please. Nothing special here. The offline application would be exactly the same, a replica of the online, probably running in Xampp or whatever you decide. The important thing is that people would not be connect to internet but they would be allowed to do the same use as if they were online, like inserting, editing and deleting their ads. 2. Database synchronization between online and offline. By the end of the day or whenever we want to, the offline website database would be synchronize with the online database. This needs to work like an incremental backup because there is no broadband where the offline database is going to be used. The ideal would be to have a script that query and export only the modified records on the offline side and another one that would import and syncronize on the online side. I don’t know if this is possible without having problems with data duplication and integrity. The script I am planning to use is called osclass, you can google it and download for free. I have a hosting server account that can be used for your tests and to install whatever is necessary. The default language is Spanish.