The HART Protocol provides specifications to facilitate two-way communication between field devices and host applications. By using Application Layer Universal Commands and Common Practice Commands, which are supported by most of the HART field devices, a host can get basic process information such as dynamic and device variables, process and/or device status, tag/long tag, etc. DD/EDD are necessary if full device information is needed.
As another part of this question, compatibility between devices is a primary objective of the HART Protocol. Many rules in Protocol ensure that a field device may be replaced with a new version of the same Device Type without disrupting system operation. Furthermore, hosts must provide the same functionality for a new Device Revision as available for the previous, supported Device Revision without requiring a software upgrade or change. With these backward and forward compatibilities, a host should support communicating with all of the devices version from HART 5 to HART 7.