A Petri Net Solution to Protocol-Level Mismatches in Service Composition This chapter models multiple web service interaction with a Petri net called Composition net (C-net). It presents Petri-net-based method to find protocol-level mismatches and then generates solutions to fix the mismatch problems. Technically, the approach consists of three steps. First, the chapter adopts BPEL for web services as the web service composition language. The BPEL description of a composite service is translated into a Petri net model. Second, a mixed-integer 624 a petri net solution to protocol-level mismatches in service composition programming formulation is used to detect the maximal empty siphons, which are then used to find protocol-level mismatches. Third, an algorithm is proposed to find siphon-based solutions for protocol-level mismatches by adding tokens in siphons to prevent them from becoming empty. Finally, time complexity comparisons are made between the approach and existing ones. The proposed one can achieve higher efficiency for resolving protocol-level mismatching issues.