Xia, Yunni, Xiang Zhang, Xin Luo, and Qingsheng Zhu. “Modelling of Ontology-Based Service Compositions Using Petri Net”. Elektronika ir Elektrotechnika 19, no. 2 (February 7, 2013): 75-78. Accessed March 1, 2021. https://eejournal.ktu.lt/index.php/elt/article/view/3474.