(a) Prerequisites to Class Representation. Before any claim or defense may be maintained on behalf of a class by one party or more suing or being sued as the representative of all the members of a class, the court shall first conclude that (1) the members of the class are so numerous that separate joinder of each member is impracticable, (2) the claim or defense of the representative party raises questions of law or fact common to the questions of law or fact raised by the claim or defense of each