Documentation for Class Dictioinary in 2nd Use Case

I. Textual Class Dictionary with Grammars.

• cd.cd
• demeter-input

II. Modification to UseCase1

1. Two edges connect Vertex from Edge, which are from and to,
   No edge connection between ConEdge and Vertex, AltEdge and AltVertex now,
   TclTk will handle the syntax problem for class dictionary;

2. Alternation class Vertex has one more alternation class -- Term,
   to support terminal class;

3. Edge has an optional part, which is a Coordinates object -- middlepoint, 
   in order to support bending point for drawing edges;

4. The content of Coordiantes has been changes from 2 DemNumber objects
   to 1 DemString object -- coords;

5. Construction edge between VertexName and Coordinates has been changed 
   to optional, making the cd grammar simpler.

III. Design Patterns Used in 2nd Use Case

   Adapter       -- Convert the interface of a class into anther
		    interface clients expect, lets classes work together
		    that couldn't otherwise because of incompatible
		    interfaces.

	Example:  Edge :   AltEdge | ConstEdge
        		*common*
          		"from"     < from > Vertex
               		[ "Bendpoints" < middlepoints > Coordinates ] 
          		"to"    < to > Vertex .



		     		  // ConstEdge is the subclass of Edge
		  ConstEdge = "ConstEdge"
            		< edgename > EdgeName .
				  // Adapt the Edge's interface to EdgeName
				     by some PPs, such as cppDrawEdges

   Facade        -- Provide a unified interface to aa set of interfaces
		    in a subsystem, defines a higher level interface that
		    makes the subsystem easier to use. 

	Example: 	 // 5 different subsystems

			(1)Graph = <edges>   Edge_List
				   <vertices> Vertex_List.

			(2)ConstEdge = <edgename> EdgeName.				       

			(3)EdgeName = <name> DemIdent
				      <e_position> Coordinates.
			(4)Coordinates = <coords> DemString.

			(5)VertexName = <name> DemIdent
					[<vn_position> Coordinates].

   Interpreter    -- Given a language, define a represention for 
		     its grammar along with an interpreter that uses the 
		     representation to interpret sentences in the language.

	Example:      the  cd.cd provided by pp group

   Iterator      -- Provide a way to access the elements of an 
		    aggregate object sequentially without exposing its 
		    underlying representation.
	
	Example:      
		      //list of edges
		   Edge_List ~ Edge { Edge }.
		    
		      //list of vertices
		   Vertex_List ~ Vertex { Vertex }.