(* Copyright (C) 2000, HELM Team.
 * 
 * This file is part of HELM, an Hypertextual, Electronic
 * Library of Mathematics, developed at the Computer Science
 * Department, University of Bologna, Italy.
 * 
 * HELM is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public License
 * as published by the Free Software Foundation; either version 2
 * of the License, or (at your option) any later version.
 * 
 * HELM is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with HELM; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place - Suite 330, Boston,
 * MA  02111-1307, USA.
 * 
 * For details, see the HELM World-Wide-Web page,
 * http://www.cs.unibo.it/helm/.
 *)


(*
 * implementazione del comando Relation 
 *)




open Union;;
open Dbconn;;
open Utility;;




let get_prop_id propl =
  let prop = List.hd propl in
  if prop="refObj" then "F"
  else if prop="backPointer" then "B"
       else assert false
;;


let relation_ex rop path rset attl =
  if path = [] then []
  else
  let usek = get_prop_id path in
  let vvar = if attl = [] then "position"
             else List.hd attl
  in	   
  let c = pgc () in
  let rset_list =  (* lista di singoletti:resource_set di un elemento *)
  (List.fold_left (fun acc (uri,l) ->
    let tv = pgresult_to_string (c#exec ("select id from registry where uri='" ^ uri ^ "'")) in
    let qq = "select uri, context from t" ^ tv ^ " where prop_id='" ^ usek ^ "' order by uri asc" in
    let res = c#exec qq in
    (List.map
    (function 
         [uri;context] -> [(uri,[[(vvar,[context])]])]
       | _ -> assert false ) 
	res#get_list) @ acc
	          )		      
        [] rset			      
  )
  in                
  let rec edup = function
      [] -> []
    | rs1::tl -> union_ex rs1 (edup tl) 
  in 
  edup rset_list 
;;