Re: how to generate alert on the values of combination of 2 prperties of a thing i.e if value of property A =5 and value of B=10 then an alert is generated(only if both conditions are satisfied.).
You can achieve a similar functionality using the DataChange event for those properties, then after verifying if you condition is met trigger some custom logic (like writing to the log or in a stream). You can't however trigger an entry in the AlertLog.
However, coming back to your question, at this moment this is not a supported functionality in ThingWorx - having an alert depending on more than one property, and with a more complex logic. I would suggest sending a ticket for enhancement request through the support.ptc.com portal.