Our software is Windows based, primarily because OPC-DA is currently the best way to communicate with PLCs and it’s Windows based. Since FactoryPMI runs on Java, you would be able to use Linux machines as clients. While I would recommend MySQL, you could easily use DB2.
Here’s what you would need:
A single Windows PC to install DB2, FactorySQL, FactoryPMI, and an OPC server on (they don’t all need to be on the same computer). You can play with free trials of both FactorySQL and FactoryPMI. They are fully functional, but limited to 2 hour runtimes that can be easily reset as many times as you wish. I would recommend downloading KepServer Ex to connect to your S7. Kepware has a similar arrangement with a free 2 hour at a time trial.
You should be able to get away with doing this project with a zero software cost. The documentation for both pieces of software is included. Post additional questions to our forum.