Most construction professionals understand "open-ends" in the context of a critical path method (CPM) schedule. Open-ends are activities that have either no predecessors or no successors. Ideally, a schedule has only two such activities on a project - a start milestone which does not have a predecessor, and a finish milestone that does not have a successor. Additional open-ends may find their way into a schedule by the way of interim milestones and/or simply a failure to add a finish activity. For example, Microsoft Project will not allow a single pair of activities to have both a start-to-start relationship and a finish-to-finish relationship, not an uncommon situation encountered in Oracle Primavera and other CPM programs. This may lead the scheduler to simply not put a successor on one of the two activities. Read more.