added cardinality for relationships

lib/deja/relationship.rb

@@ -3,7 +3,7 @@ class Relationship < Model
     attr_accessor :start_node, :end_node
 
     class << self
-      attr_reader :directionality
+      attr_reader :directionality, :cardinality
 
       @directionality = {}
 
@@ -18,6 +18,8 @@ def from(from_type=nil, opts={})
         @directionality ||= {}
         @directionality[from_type] ||= []
         @directionality[from_type] << to_type
+
+        @cardinality = opts[:cardinality] || nil
       end
 
       def valid_direction?(from_type=nil, to_type=nil)
@@ -33,6 +35,10 @@ def label
         return self.name.underscore.to_sym
       end
 
+      def cardinality
+        @cardinality
+      end
+
       def find(id_or_index)
         relationship = Deja::Query.load_relationship(id_or_index)
         relationize(relationship)