I need to calculate the downtime of various critical systems (think telephony, website, etc.):
Per business process affected
Overall for the organization
Per month and YTD.
Why it's complicated:
Some systems need to be up 24/7 (website, for example) and others during specific periods (operating hours): the sales DB might need to be up 8:00 to 20:00 Mon-Fri, 9:00 to 15:00 Saturday and closed on Sundays whereas telephony and intranet would be 7:00 - 22:00 7 days/week, etc.
Some downtime events might be over more than one calendar day and those days may have different operating hours.
Some events affect more than one system, and those systems might have different operating hours.
Some events affect more than one business process.
Schedules might change during the year
Here's a sample of data I have at this point: (I do have a date dimension table and can create a time dimension table as well)
Systems to Business process mapping
Systems operating hours
Everything I found so far is for simple, fixed hours workdays with the only twist being weekends/holidays.