dim_ref 
  [classification_clause]...
  KEY  
    {[(] [alias.] fact_column  [)] 
     |
     (  [alias.] fact_column [, [alias.] fact_column]... )
    }
  REFERENCES 
     {[(]  attribute  [)] 
      | 
      ( attribute [, attribute]... )
     }   
  HIERARCHIES ( hier_ref [, hier_ref]... )