One of the most confusing things about the Oracle BPM Workspace is the effect of claiming work items by end users. 

Claiming a work item instance is useful to allow several people with a shared assignment group of instances to work independently without worrying about conflicting with one another.  As a user, I can claim a work item over a period of time, go to lunch, and work on the instance again when I return without others completing it while I was away.

Unless already claimed, when one or more work items are selected in the Workspace they can be claimed by that user.

As shown below, the “Acquired By” column in the Workspace lets end users see who has a work item claimed.    

If another user is assigned to the same work item, that user can still view the work item in their worklist.   Once the work list has been refreshed, if the work list has the “Acquired By” column displayed, any user assigned to the work item can see who has claimed the work item.   If the work item is selected, they are still able to view the instance, but because the work item has already been claimed by another user, the buttons that would ordinarily have allowed the user to approve the work item are not shown.

Process Owner and Claimed Work Item Instances

If a user is a Process Owner for the project however, the effect of a work item being claimed is overridden.  As shown below, James Cooper is a process owner, and even though the instance has already been claimed by another user (John Steinbeck), the process owner still has the buttons enabled for this work item.  Additionally, a process owner can “Release” a work item instance that has been claimed by another user so that it is available to be worked upon by other users assigned to the work item.