anchor.diff:  
   + `entities`: a list of entites to search for. Each entity is represented by a JSON object with the
     following elements:
  -    + `id` or `idPattern`: Id or pattern of the affected entities. Both cannot be present at the
  -      same time, but one of them must be.
  -    + `type`: specifies the type of the entities to search for. If omitted, it means
  -      "any entity type".
  +    + `id` or `idPattern`: Id or pattern of the affected entities. Both cannot be used at the same
  +      time, but at least one of them must be present.
  +    + `type` or `typePattern`: Type or type pattern of the entities to search for. Both cannot be used at
  +      the same time. If omitted, it means "any entity type".
   + `attributes`: a list of attribute names to search for. If omitted, it means "all attributes".
   + `scopes`: a list of scopes to restrict the results of the query. Each scope is represented by a
     JSON object with a `type` (a JSON string) and a `value` (whose type depends on the `type`
  
positive.code:     
      + type: Room (optional, string) -  comma-separated list of elements.
        Retrieve entities whose type matches one of the elements in the list.
  
      + idPattern: Bode_.* (optional, string) - A correctly formated regular expression.
        Retrieve entities whose ID matches the regular expression. Incompatible with id.
      
      + q: temperature>40 (optional, string) - A query expression, composed of a list of statements
        separated by `;`, i.e., q=statement;statements;statement.
  
negative.code: 
  The payload may contain the following elements (all of them optional):
  
  + `entities`: a list of entites to search for. Each element is represented by a JSON object with the
    following elements:
      + `id` or `idPattern`: Id or pattern of the affected entities. Both cannot be used at the same
        time, but at least one of them must be present.
      + `type` or `typePattern`: Type or type pattern of the entities to search for. Both cannot be used at
        the same time. If omitted, it means "any entity type".
  + `attributes`: a list of attribute names to search for. If omitted, it means "all attributes".
  + `scopes`: a list of scopes to restrict the result of the query. Each scope is represented by a
     JSON object with a `type` (a JSON string) and `value` (whose type depends on the `type`
  