Paulo J. F. Carreira Helena Galhardas Antónia Lopes João Pereira Extending Relational Algebra to express one-to-many data transformations. 145-159 2005 conf/sbbd/2005 SBBD http://www.sbbd-sbes2005.ufu.br/arquivos/artigo-10-CarreiraGalhardas.pdf db/conf/sbbd/sbbd2005.html#CarreiraGLP05