D2L posted their explanation of filing for this "Declaratory Judgment" against Blackboard. This action is an attempt to prevent Blackboard from further lawsuits against D2L under their latest patent ('853). D2L is formally appealing to the courts for protection due to "the existence of substantive, actual controversy".
From D2L's complaint:
This history of Blackboard’s strategy of litigation and intimidation creates a substantial controversy between D2L and Blackboard of sufficient immediacy and reality to warrant the issuance of a declaratory judgment as to the noninfringement and invalidity of the ’853 patent.