This is a challenge to identify the downtime of servers from the log data generated by a monitoring application.

There is a monitoring application that keeps checking the status of several servers at 5 minute intervals. When the monitoring application finds that a particular server is down, it adds a record into the log table.

You can get more information at the T-SQL Challenge #37 blog post: http://beyondrelational.com/blogs/tc/archive/2010/08/23/tsql-challenge-37-calculate-the-downtime-and-duration-of-servers-based-on-the-monitoring-log.aspx