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For each data point that matches an HA’s “point of concern”, it inspects the next K local data points in the local database (where K is the supplied “notification threshold count”). If more than M% of these matched “points of concern” with the same Health Authority (where M is tthe the “notification threshold percent”), then it generates an exposure notificationall K data points are classified as part of the exposure notification for that day.
To determine the duration of the exposure notification , the same for a given day, this calculation is repeated for each data point that matches a point of concern. Exposure notifications that overlap are combined together to create an overall exposure duration.
To illustrate, this diagram shows a series of data points, some of which match, and some of which do not match any points of concern. The brackets on the left indicate the groups of 6 data points that match more than 66% (4 points). The brackets on the right show the overall Exposure Duration that is derived.
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performed for all data points in the day - with all data points that are classified as part of an exposure contributing 5 minutes to the total exposure reported for the day.
There can only be one exposure notification in a day, and the miniumum exposure perios is (5 mins x “notification threshold count”)
See more details here: Exposure Notifications more detailed design
Related Work
In MVP1, under SAF-397 / MVP1#17, we will be doing work to reduce the volume of data downloaded by the Mobile App from Same Places.
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