Question 2:
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Class dictionary design

Consider the following input and the corresponding cd.
Find the UNKNOWNs.

module
  di TreeICG(ElementICG e) { 
    Tree : Leaf | Branch .
    Leaf = Data @ e.
    Branch = Data @ e ListOfTree.
    ListOfTree : Empty | NonEmpty.
    Empty = .
    NonEmpty = <f> Tree <r> ListOfTree.
  } 
  aspect TreeWalker { 
    declare strategy
    declare traversal
    declare constraints
  }
  // visitor classes
end
module
  di ElementICG { 
    Data = Name_ValuePair_List.
    NameValuePair = Name Value.
    Name = .
    Value = .
    Name_ValuePair_List : Empty | NonEmpty.
    Empty = .
    NonEmpty = <f> NameValuePair <r> Name_ValuePair_List.
  }
  aspect ElementWalker { 
    declare constraints
    declare strategy
    declare traversal
  }
  // visitor classes
end
module
  di Decide {
    F = Constraints.
    Constraints : E | N.
    E = .
    N = <f> Constraint <r> Constraints.
    Constraint = RelNumber <v1> Variable <v2> Variable.
    RelNumber = int.
    Variable = .
  }
  aspect Chooser {
    declare strategy
    declare constraints
    declare traversal
  }
end
cd XMLSubset implements TreeICG(ElementICG) {
  XMLDef = A <b> B.
  A : X | Y common <u> U V.

  map treeMap = for TreeICG { 
   use Tree as XMLDef
   use Leaf as EmptyTag
  }
  map elementMap = for ElementICG {
   use Data as OpenTag
   use Data as OpenCloseTag
  }
}

Here comes the cd:
==================================================

Input =
 List(Module)
 ConcreteCd EOF.
Module = "module" 
 UNKNOWN List(UNKNOWN) 
 // list of visitor classes
"UNKNOWN". 
DI = "di" DIName [UNKNOWN] "{" UNKNOWN "}".
ParameterDI = "(" DIName DIVariable ")".
Aspect = "aspect" AspectName 
  UNKNOWN.
Declaration UNKNOWN.
Strategy UNKNOWN.
Traversal UNKNOWN.
Constraints UNKNOWN.

ConcreteCd = "cd" CDName "implements" DIName [ActualDI] 
  "{" UNKNOWN "}".
ActualDI = "(" DIName ")".
Map = "map" MapName "=" "for" DIName UNKNOWN(Basic). 
Basic = "use" <use> Cd_Vertex "as" <as> Cd_Vertex.

Cd_Graph = UNKNOWN. // this is a big UNKNOWN
Cd_Vertex = < vertex_name > Cd_ClassName ["@" DIName] .

DIName = Ident.
DIVariable = Ident.
AspectName = Ident.
CDName = Ident.
MapName = Ident.

List(S) ~ {S}.
CList(S) ~ "{" {S} "}".
Main = <s> String.