The Indicator Lights Interface 33These nine indicators appear in a small window that measures about 1” x 2” on the user’sdisplay. These indicators require a modest amount of screen real estate, a resource that isprecious to users, during normal operation. Because the expected benefit of the indicatorsoutweighs its cost in screen real estate, I expect the user will keep this indicator windowvisible at all times. Note, however, that while the user investigates a problem indicated bythe interface, the screen real estate requirements increase. This change in resourceconsumption is appropriate during periods when the user is actively engaged with theinterface [8].Each indicator light can signal one of four states about the subsystem it monitors:x Operating normallyx Developing a problem or experiencing a noncritical problemx Experiencing a critical problemx Indicator not operational or status unknownThe first three of these states are color coded to one of three urgency levels: normal,warning, and critical. By default, the colors associated with these urgency levels aregreen, yellow, and red. I chose this color scheme to make it easy for users to remembersince green, yellow, and red correspond to the colors used to signify similar meanings inmany situations in the United States—most notably traffic signs and signals. This colorscheme is not without its own difficulties. For instance, some users may be using amonochrome monitor, others may be color blind, and not all cultures use green, yellow,and red for these meanings. For these reasons, the user can easily customize the colorscheme used to represent these three urgency levels. In fact, the user can forego the useof color and instead use different grayscale levels to signify the different urgency levels.Figure 4.1 shows two views of the indicator window: one in the default green-yellow-redcolor scheme and one in a monochrome scheme.8 (a) Color Scheme (b) Monochrome SchemeFigure 4.1: Indicator LightsThis figure shows two views of the indicator lights. The indicator lights give users aperipheral awareness of system state. View (a) shows the default green-yellow-red colorscheme. View (b) shows a monochrome scheme. In both views, the Tokens andNetwork indicators are shown with a warning urgency level and the Space and Taskindicators are shown with a critical urgency level. All other indicators are normal. 8 A color supplement to this thesis is available at http://www.cs.cmu.edu/Reports34 Interacting with the UserIn this section, I present each of the nine indicator lights and their associated informationalwindows. For each indicator, I begin by describing its purpose and the meaning of itscolor changes. I then describe the layout and operation of each window associated withthat indicator. Some of these indicators (Control Panel, Tokens, Advice, Hoard Walk, andTask) have multiple supporting windows. Others (Space, Network, Reintegration, andRepair) have just a single one. I begin the presentation with the Control Panel indicatorand all of its supporting windows, and continue through the other indicators in the ordershown in Figure 4.1.4.2 Control PanelThe first indicator light, a special case, does not actually indicate problems to the user (it isalways green). Instead, it gives the user a way to control the handling of events, thecolors of the urgency levels, the physical and logical connectivity to servers, and otherbehaviors of the interface. In the sections that follow, I will explore each aspect of thecontrol panel.4.2.1 Event ConfigurationWhen the user double-clicks on the Control Panel indicator, the Event Configurationwindow (one tab of the control panel window) appears. From this window (shown inFigure 4.2a), the user can customize event notification. In particular, the user can specifywhether or not she wants to be notified of a particular event. If so, she can specify howthe system will indicate its occurrence to her. Her notification options range fromautomatically popping up the appropriate window to quietly changing the color of thegiven indicator light.The layout of this window organizes the events by the indicator that signals them. Thus,only those events associated with the selected indicator can be chosen, and selecting adifferent indicator changes the list of events that can be chosen. Once an event is selected,the user can change its configuration using the right-hand side of the window. The usermust first decide whether or not she wishes to be notified of this event. If she chooses notto be notified, all of the other selections are grayed out. If she chooses to be notified, shemust then define the urgency of the event and how she wishes to be alerted to this event.The minimum (and default) action the system takes to alert the user of an event is tochange the color of the event’s indicator to reflect the urgency of the event (e.g., red,yellow, or green). In addition, the user can customize the alert to pop up the appropriatewindow automatically, to beep, and/or to flash the indicator light on and off a few times.Control Panel 35 (a) Event Configuration Tab (b) Urgency Colors Tab (c) Physical Connectivity Tab (d) Logical Connectivity Tab(e) Behavior TabFigure 4.2: The Tabs of the Control PanelThis figure shows the supporting windows that appear when the Control Panel indicatoris double-clicked. From these windows, the user can control various aspects of theinterface. The Event Configuration tab, view (a), allows the user to control the wayevents are notified. The Urgency Colors tab, view (b), allows the user to customize thecolor scheme used to indicate the three levels of urgency. The Physical Connectivitytab, view (c), allows the user to control connectivity to each Coda server. The LogicalConnectivity tab, view (d), allows the user to control the servicing of cache misses andthe propagation of updates while remaining fully connected to the network. TheBehavior tab, view (e), allows the user to disable confirmation dialogue boxes.36 Interacting with the User4.2.2 Urgency ColorsIf the user clicks on the Urgency Colors tab of the Control Panel, she will see the windowthat appears in Figure 4.2(b). From this window, the user can choose what colors theinterface will use to indicate each of the different urgency levels. By default, the normalurgency level is indicated by the color green, the warning