Infopath date calculations

Hi Ragavendar,
I presume you areworking with some kind of appoinment system.
So, what we have to do here is ,
Create rules for both the start and end date fileds as after selecting any date, it will check with the current list's existing data by quiring them, and show an message if needed.

To make it more easy, get all the data of the list on load. And in the certain rules, just qury the data and check.

Hope it will help.