Constraint Date vs Due Date
Accepted answer
I am not certain, but I think due date is simply a timestamp attribute that is used to store a due date for a work item, while constraint date (and type) are used in planning/scheduling. See links below for related information:
The following link shows an example on extending the use of due date:
https://jazz.net/forum/questions/109071/due-date-vs-finish-no-later-than-whats-the-differences
https://jazz.net/library/article/657
https://jazz.net/library/article/663
The following link shows an example on extending the use of due date:
https://rsjazz.wordpress.com/2015/10/16/due-date-notifier-an-asynchronous-task-example/