Modern workflow management systems have to support tasks with complex dependency constraints and to cope with resource allocation problem. Therefore the need for analysis method to verify the correctness of workflow specification is becoming crucial. This paper exploits recent advances of structure theory of Petri nets to find efficient structural characterization of the basic soundness property. The obtained results allow the identification and analysis of workflow net classes allowing the modelling of complex synchronization and routing workflow constructs of practical need in particular in the context of collaborative management systems. For further information, please visit this web site.