LLORET, J. and WIRATUNGA, N. 2015. Survey state model (SSM): XML authoring of electronic questionnaires. In Kosek, J. (ed.) XML Prague 2015 conference proceedings. Hájích, Czech Republic: Ing. Jiří Kosek [online], pages 159-178. Available from: https://archive.xmlprague.cz/2015/files/xmlprague-2015-proceedings.pdf