The task itself should be focused on just completing that specific activity and  nothing else. To help ensure that effect took keeping a general design rule of no  more than five steps within a task definition. There will always be exceptions, and  a task itself could run a traditional business process. However, in general, the  maximum five-step rule helps you design the correct types of tasks. Note:  This design approach enables for tasks to be truly focused on specific  business activities and the relationships between the activities. This can also  enable task reuse. If a specific business activity is part of a larger task, that  specific task cannot be used within the case lifecycle as needed without  running the entire defined process. As shown in Figure 18-2 on page 560, there are several external entities that the  case interacts with. The intent in this section is to outline those types of  interactions. These interactions are all system-based, because the user  interactions are covered from a task perspective and user interface (UI)  perspective. The following list includes some of the entities where interactions are required: For each entity, a list of specific interactions must be created. This falls into a  more technical type of design, and is covered in more detail in 18.4, “High-level  design” on page 580. The next aspect of interactions to be determined is at the role level, which ties  people into the identified entities and activities. These are the basic roles that we  have defined:  Chapter 18. Complex use case scenario  565 GLYPH<SM590000> Clerical Staff GLYPH<SM590000> Medical Staff (at this point in the design, it is unknown if this role must be  broken down into more specific roles) GLYPH<SM590000> Nurse (at this point, it is unknown if the Nurse role must be broken down into  more specific roles) GLYPH<SM590000> Doctor GLYPH<SM590000> Medication GLYPH<SM590000> Procedures GLYPH<SM590000> Labs and tests GLYPH<SM590000> Documentation GLYPH<SM590000> Billing GLYPH<SM590000> Electronic medical records (EMR) GLYPH<SM590000> Calendaring Case interaction