(forum thread http://forums.rhq-project.org/viewtopic.php?f=5&t=46 talks about the use-cases involved)

Suppose I have a managed resource ("Product X") that for one reason or another cannot be auto-discovered. The only way it can make it into inventory is via manual-discovery. The user enters the plugin configuration needed to connect to Product X and the plugin's discovery component will take that config and be able to detect the Product X resource and create a discovery details object for it (including Product X's version string). From there, an inventory report is sent to the server and the new Product X resource is added to inventory.

Now, suppose sometime later, someone upgrades Product X. It was version 1.0, but it has now been upgraded to version 2.0.

Today, there is no way for the plugin container to detect this version change.  Since Product X can never be auto-discovered, it never goes through the periodic server scan processing that would normally update version strings that get auto-detected. Product X was manually discovered, so it never gets periodically discovered again. Therefore, there is no way for Product X resource's version string to ever be anything other than its very first, originally discovered version.

We need a way to periodically check manually discovered resources for changes like this.