paper's Title: Assembler authors: Federico Balaguer, Gaston Dombiak e-mail: [fede,gaston]@sol.info.unlp.edu.ar postal mail: cc11 (1900) La Plata - Buenos Aires - Argentina phone/fax: (54) 21 22-8252 Abstract There are many situations in which the need to group a set of object into another one, forces the creation of a new abstraction or object. It is not possible to use Collections (which are provided for many OO languages ) because there are some behavior that has to be assigned to the new object. Also,it is possible to identify some criteria to group and calculations, all of which compound the behavior and knowledge of the new object. We found this problem many times in different domains such as: financial trading support applications and geographical information systems design. This paper presents our solution for this "recurrent" problem. Subject Area: Transactional Objects Keywords: grouping, builder, visitor