Blackboard's Patent Claim in a Nutshell

Diagram 1 (Pre-Blackboard: Course Islands) represents the state of affairs, according to Blackboard, prior to their purported invention. Course Management Systems consisted of a "bunch of separate web sites" for each class. You had to have a "different login, different central space, new calendar, new inbox, etc" for every course.

Diagram 2 (Blackboard's Invention) represents Blackboard's purported invention. Blackboard supposedly came up with the idea whereby users could logon to their central space, could see all their courses from one central space, and move from one course to another behind a single logon. A user can also have multiple roles. In other words, the same user could be a student in one course and an instructor in a different course.

Recall that a patent provides ownership for an Idea. In this instance Blackboard claims that it originated the idea of a course management system that provides unified access ("user centric") to course material across multiple courses and also provisions for multiple roles across multiple courses. If your system implements this basic idea (D2L certainly does), then more than likely you are infringing on Blackboard's patent.