Simultaneous events are usually a source of modeling errors, not only for this is a difficult concept to capture, but also because current modeling methodologies usually do not provide good solutions for the problem. This topic has been subjected to a large number of discussion and solutions. Most common approaches are based on the assignment of static priorities to events, activities, or processes, in, respectively, event, activity and process world views. In modular methodologies a common approach is to assign priorities to components. Recently, these modeling formalisms have introduced the possibility for handling simultaneous events at the same time, i.e., in parallel. Parallelism removes the difficult task of assigning priorities to models. Dynamic structure models introduced a new dimension to this subject: how to define model structure when simultaneous transitions occur. The parallel dynamic structure discrete event formalism offers both a simple and powerful solution to this problem and the advantage of removing ambiguity when structural changes occur.