During the design of any information system, it is important to balance between flexibility and support. This is of particular importance when designing process-aware information systems. On the one hand, userswant to have support from the system to conduct their daily activities in a more efficient and effective manner. On the other hand, the same users want to have flexibility, that is, the freedom to do whatever they want and without being "bothered" by the system. Sometimes it is impossible to provide both flexibility and support because of conflicting requirements. The continuous struggle between flexibility and support is illustrated by Fig. 6.1. The right-hand-side of Fig. 6.1 shows the part of the spectrum covered by classical workflow management systems. These systems focus on processes that are repeatedly executed in some predefined manner and are driven by procedural languages. Note that in procedural workflow models there may be alternative paths controlled by (X)OR-splits/joins. However, the basic idea is that the completion of one task triggers other tasks. The YAWL nets described in earlier chapters provide such a procedural language. Although the YAWL language is highly expressive, its token-based semantics is most suitable for repetitive processes with tight control. The left-hand-side of Fig. 6.1 shows the other end of the spectrum. Here processes are less repetitive and the emphasis is on flexibility and user empowerment. Here it is difficult to envision all possible paths and the process is driven by user decisions rather than system decisions. Groupware systems (e.g., "enhanced" electronic mail, group conferencing systems, etc.) support such processes and focus on supporting human collaboration and co-decision. Groupware systems do not offer supportwhen it comes to ordering and coordination of tasks. Instead, the high degree of flexibility of these systems allows users to control the ordering and coordination of tasks while executing the process (i.e., "on the fly").