This is the mapping as ERA tree for the query:

This is the mapping information for the query:

      [ JOIN
         [ UNION
            [ UNION
               [ PROJECTION
                  [ F-TRANS
                     dbHotels.hotels
                     [  Price ] 
                       [ observer.transformFunctions.Currency.dolar2euro ]
                  ]
                  [  dbHotels.hotels.name dbHotels.hotels.price ]
               ] ( T1 )
               [ PROJECTION
                  [ F-TRANS
                     XMLHotels.hotels
                     [  Price ] 
                       [ observer.transformFunctions.Currency.dolar2pound ]
                  ]
                  [  XMLHotels.hotels.name XMLHotels.hotels.price ]
               ] ( T2 )
                ( T1.Name T2.Name ) ( T1.Price T2.Price )
            ] ( T3 )
            [ PROJECTION
               [ F-TRANS
                  WebSearchHotels.hotels
                  [  Price ] 
                    [ observer.transformFunctions.Currency.dolar2dkcrown ]
               ]
               [  WebSearchHotels.hotels.name WebSearchHotels.hotels.price ]
            ] ( T4 )
             ( T3.Name T4.Name ) ( T3.Price T4.Price )
         ] ( ALIAS6 )
         [ JOIN
            [ UNION
               [ UNION
                  [ PROJECTION
                     dbHotels.hotels
                     [  dbHotels.hotels.name dbHotels.hotels.location ]
                  ] ( T1 )
                  [ PROJECTION
                     XMLHotels.hotels
                     [  XMLHotels.hotels.name XMLHotels.hotels.location ]
                  ] ( T2 )
                   ( T1.Name T2.Name ) ( T1.Location T2.Location )
               ] ( T3 )
               [ PROJECTION
                  WebSearchHotels.hotels
                  [  WebSearchHotels.hotels.name WebSearchHotels.hotels.location ]
               ] ( T4 )
                ( T3.Name T4.Name ) ( T3.Location T4.Location )
            ] ( ALIAS4 )
            [ JOIN
               [ UNION
                  [ UNION
                     [ PROJECTION
                        dbHotels.hotels
                        [  dbHotels.hotels.name dbHotels.hotels.name ]
                     ] ( T1 )
                     [ PROJECTION
                        XMLHotels.hotels
                        [  XMLHotels.hotels.name XMLHotels.hotels.name ]
                     ] ( T2 )
                      ( T1.Name T2.Name ) ( T1.Name T2.Name )
                  ] ( T3 )
                  [ PROJECTION
                     WebSearchHotels.hotels
                     [  WebSearchHotels.hotels.name WebSearchHotels.hotels.name ]
                  ] ( T4 )
                   ( T3.Name T4.Name ) ( T3.Name T4.Name )
               ] ( ALIAS2 )
               [ JOIN
                  [ UNION
                     [ UNION
                        [ SELECTION
                           dbHotels.hotels
                           [ AND [ >= dbHotels.hotels.units 1 ] [ = dbHotels.hotels.building "collective" ] ]
                        ] ( T1 )
                        [ SELECTION
                           XMLHotels.hotels
                           [ AND [ >= XMLHotels.hotels.units 1 ] [ = XMLHotels.hotels.building "collective" ] ]
                        ] ( T2 )
                         ( T1.Name T2.Name ) ( T1.Location T2.Location ) ( T1.Meals T2.Meals ) ( T1.Building T2.Building ) ( T1.Facilities T2.Facilities ) ( T1.Units T2.Units ) ( T1.Price T2.Price ) ( T1.Stars T2.Stars )
                     ] ( T3 )
                     [ SELECTION
                        WebSearchHotels.hotels
                        [ AND [ >= WebSearchHotels.hotels.units 1 ] [ = WebSearchHotels.hotels.building "collective" ] ]
                     ] ( T4 )
                      ( T3.Name T4.Name ) ( T3.Location T4.Location ) ( T3.Meals T4.Meals ) ( T3.Building T4.Building ) ( T3.Facilities T4.Facilities ) ( T3.Units T4.Units ) ( T3.Price T4.Price ) ( T3.stars T4.stars )
                  ] ( ALIAS0 )
                  [ SELECTION
                     [ UNION
                        [ UNION
                           [ PROJECTION
                              [ F-TRANS
                                 dbHotels.hotels
                                 [  price ] 
                                   [ observer.transformFunctions.Currency.dolar2euro ]
                              ]
                              [  dbHotels.hotels.name dbHotels.hotels.price ]
                           ] ( T1 )
                           [ PROJECTION
                              [ F-TRANS
                                 XMLHotels.hotels
                                 [  price ] 
                                   [ observer.transformFunctions.Currency.dolar2pound ]
                              ]
                              [  XMLHotels.hotels.name XMLHotels.hotels.price ]
                           ] ( T2 )
                            ( T1.Name T2.Name ) ( T1.Price T2.Price )
                        ] ( T3 )
                        [ PROJECTION
                           [ F-TRANS
                              WebSearchHotels.hotels
                              [  price ] 
                                [ observer.transformFunctions.Currency.dolar2dkcrown ]
                           ]
                           [  WebSearchHotels.hotels.name WebSearchHotels.hotels.price ]
                        ] ( T4 )
                         ( T3.Name T4.Name ) ( T3.Price T4.Price )
                     ]
                     [ = dbHotels.hotels.price 200 ]
                  ] ( ALIAS1 )
                  [ = ALIAS0.name ALIAS1.name ]
               ] ( ALIAS3 )
               [ = ALIAS2.name ALIAS3.name ]
            ] ( ALIAS5 )
            [ = ALIAS4.name ALIAS5.name ]
         ] ( ALIAS7 )
         [ = ALIAS6.name ALIAS7.name ]
      ]
        f: NULO