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Subject: CAP Use Scenarios Draft
Friends - As I went back to the books on writing use cases, I realized that design use cases are very useful for describing processes, but not quite so handy for describing events, which is really what individual messages are. So what I'm offering here for your discussion aren't so much use cases (except perhaps in the dreaded "business use case" sense!) as they are just illustrations of some potential real-world applications. - Art ---------------- Use Scenarios - Common Alerting Protocol Message Format draft 5/11/2003 The following scenarios illustrate a few possible use cases for the Common Alerting Protocol message format. [Note that at this point we are discussing only the message itself, not the telecommunications or applications architecture(s) that support(s) it.] I - Manual Origination The Incident Commander at an industrial fire with potential of a major explosion decides to issue a public alert with three components: a) An evacuation of the area within half a mile of the fire; b) a shelter-in-place instruction for people in a polygon roughly describing a downwind dispersion "plume" extending several miles downwind and half a mile upwind; and c) a request for all media and civilian aircraft to remain above 2500 feet above ground level when within half a mile of the incident. Using a portable computer and a web page (and a pop-up drawing tool to enter the polygon) the Incident Commander issues the alert as a CAP message to a local alerting network. II - Automated Origination by Sensor System Along a popular Northwest beach a series of automatic tsunami sirens have been installed. In the base of each siren is an accelerometer and a computer with a GPS receiver. All of these devices are linked by a wireless local area network. When an individual unit detects what appears to be a P-wave/S-wave sequence that might indicate a near-shore earthquake, it generates a CAP message containing its location, the precise time of the P-wave's arrival, and the estimated distance of the epicenter based on the P-wave/S-wave interval. Each computer in the network correlates all the messages received from the other instruments (which form what amounts to a phased array) and, if the pattern of messages suggests a near-shore quake (and not just a truck driving down the coastal highway) then each siren activates. In addition, one of the instruments assembles a "summary" CAP message describing the event and feeds it to regional and national seismic networks. (Based on an idea shared by David Oppenheimer at the USGS in Menlo Park.) III - Aggregation and Correlation on Real-time Map At the State Operations Center a computerized map of the state depicts, in real time, all current and recent warning activity throughout the state. All major warning systems in the state... the Emergency Alert System, siren systems, telephone alerting and other systems... have been equipped to report the details of their activation in the form of a CAP message. (Since many of them are now activated by way of CAP messages, this is frequently just a matter of forwarding the activation message to the state center.) Using this visualization tool, state officials can monitor for emerging patterns of local warning activity and correlate it with other real time data (e.g., telephone central office traffic loads, 9-1-1 traffic volume, seismic data, automatic vehicular crash notifications, etc.) IV - Integrated Public Alerting As part of an integrated warning system funded by local industry, all warning systems in a community can be activated simultaneously by the issuance by authorized authority of a single CAP message. Each system converts the CAP message data into the form suitable for its technology (text captioning on TV, synthesized voice on radio and telephone, activation of the appropriate signal on sirens, etc.) Systems that can target their messages to particular geographic areas implement the targeting specified in the CAP message with as little "spill" as their technology permits. In this way, not only is the reliability and reach of the overall warning system maximized, but citizens also get corroboration of the alert through multiple channels, which increases the chance of the warning being acted upon. V - Repudiating A False Alarm Inadvertently (or perhaps not, but that will be the subject of investigation later on) the integrated alerting network has been activated with an inaccurate warning message. This activation comes to officials' attention immediately through their own monitoring facilities (e.g., III above). Having determined that the alert is, in fact, inappropriate, the officials issue a cancellation message that refers directly to the erroneous prior alert. Alerting systems that are still in the process of delivering the alert (e.g., telephone dialing systems) stop doing so. Broadcast systems deliver the cancellation message. Other systems (e.g., highway signs) simply reset to their normal state. --------------------------
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