The Case Study: The HOLIS Use Cases

Let's see how we can apply use cases in our case study. In Chapter 7, the HOLIS team applied systems engineering as a problem analysis technique to better understand the systems architecture and design constraints for HOLIS, our state-of-the-art home lighting automation system. During that process the team produced the context diagram for the system (Figure 14-7).

Figure 14-7. HOLIS context diagram

Figure 14-4. Storyboard slide for step 2 of a use case

Figure 14-5. Storyboard slide for step 3 of a use case

Find the HOLIS Actors

In building the use-case model for the system, the team first revisited the actors, those external users and devices that exist outside the system and interact with the system under development. The process resulted in the discovery of some new actors for the system. Table 14-1 shows the updated list of HOLIS actors (with new names given to a few of the actors identified earlier).

Find the HOLIS Use Cases

The team then held a brainstorming session to identify the primary HOLIS use cases and wrote a brief description for each one. Among others, they identified a simple use case they called "Turn Light On/Off" and described it as follows .

Table 14-1. Revised List of HOLIS System Actors

Actor	Description
Homeowner /Programmer	This is the homeowner or other operator who programs the various features, lighting scenes, and so on for HOLIS, using either the optional PC Programmer or the Central Control Unit.
Resident	This is the actor we use to describe how any person interacts with the system on a daily-usage (nonprogramming) basis.
Emergency Receiver	When an emergency signal is activated by a resident, a phone call is made to this actor.
Light Bank	This actor is a set of light banks grouped together for common action.
Wireless Remote Controller	The system also accepts control inputs from IEEE 802.11b (Wi-Fi) standard wireless remote control devices, which also serve as an actor on the system.
Lumenations Services	This actor is a Lumenations, Ltd., service person who accesses the system remotely for remote programming and maintenance service operations.
Motion Sensor	Motion sensor inputs are also actors on the system.

Associate the Actors and Use Cases

After identifying each of the primary use cases for the system, the team built a visual use-case model to illustrate the relationships between the actors and the various use cases with which the actors interact. Figure 14-8 shows a portion of that model.

Figure 14-8. A portion of the HOLIS use-case model

Outline the Use Cases

Over the course of development, the team proceeded to outline and then further elaborate each of the use cases identified in the use-case model by building a name , description, and initial flow of the events outlined for each use case. That's the appropriate level of detail for the HOLIS project at this time. We'll revisit the "Turn Light On/Off" use case again later in Chapter 21, Refining the Use Cases.