Re: 3 value logic. Why is SQL so special?

"JOG" <jog_at_cs.nott.ac.uk> writes:
> So an aircraft might not take off and yet it has a departure time
> attribute? That makes absolutely no sense at all.

i think the characteristic was scheduled departure time. scheduled departure time can be useful for a number of things.

commercial aircraft tend to have scheduled departure times (helps give you an approx idea when to show up at the airport) ... as well as scheduled arrival times.

at one time the FAA didn't interfer with departure times ... and let aircraft circle if weather cut down on capacity of airfield landing rates. at some point the FAA started holding plane departures if there was predictions about reduced capacity to land the plane.

you frequently hear pilots making announcements about particular arrival being ahead of time or late ... which is the difference between the scheduled arrival time and the actual arrival time. both the actual arrival time and the difference (early/late) between the actual arrival time and the scheduled arrival time ... aren't actually known until near to the time that the plane actually arrives.

in the routes database used for scheduling reservations involving connecting flights ... there typically is an attempt to match scheduled arrival time to connecting scheduled departure time (within some fudge factor).

however as anybody who has had a late arrival and missed their connecting flight ... the scheduled arrival time and the actual arrival time may be different. also some carriers when they see that their are a significant connecting passengers ... on a flight there is starting to show a predicted late arrival time ... may attempt to delay the departure of some number of flights as convinience to connecting passengers. however, this can have cascading effects if the connecting departing flight then impacts other passengers that have connecting flights at the next arrival.

lots of flights that have significant, long term differences between scheduled arrival and actual arrival may indicate various loading and capacity issues and reason to update projected schedules. changes in projected specific schedules then can have cascading effects with regard to scheduling departure/arrivals for purposes of route and load planning involving connecting flights.

various past posts mentioning 3-value logic

http://www.garlic.com/~lynn/2003g.html#40 How to cope with missing values - NULLS?
http://www.garlic.com/~lynn/2004f.html#2 Quote of the Week
http://www.garlic.com/~lynn/2004l.html#75 NULL
http://www.garlic.com/~lynn/2005.html#15 Amusing acronym
http://www.garlic.com/~lynn/2005b.html#17 [Lit.] Buffer overruns
http://www.garlic.com/~lynn/2005i.html#35 The Worth of Verisign's Brand
http://www.garlic.com/~lynn/2005m.html#19 Implementation of boolean types
http://www.garlic.com/~lynn/2005t.html#20 So what's null then if it's not nothing?
http://www.garlic.com/~lynn/2005t.html#23 So what's null then if it's not nothing?
http://www.garlic.com/~lynn/2005t.html#33 What ever happened to Tandem and NonStop OS ?
http://www.garlic.com/~lynn/2005u.html#12 3vl 2vl and  NULL
http://www.garlic.com/~lynn/2006e.html#34 CJ Date on Missing Information

various past posts mentiong working with OAG database of all (world-wide) commercial schedule flight segments as part of airline res system (over 4k airports and over 400k commercial scheduled flight segments)

http://www.garlic.com/~lynn/99.html#136a checks (was S/390 on PowerPC?)
http://www.garlic.com/~lynn/2000f.html#20 Competitors to SABRE?
http://www.garlic.com/~lynn/2001d.html#69 Block oriented I/O over IP
http://www.garlic.com/~lynn/2002g.html#2 Computers in Science Fiction
http://www.garlic.com/~lynn/2002j.html#83 Summary: Robots of Doom
http://www.garlic.com/~lynn/2003o.html#17 Rationale for Supercomputers
http://www.garlic.com/~lynn/2004b.html#6 Mainframe not a good architecture for interactive workloads
http://www.garlic.com/~lynn/2004o.html#23 Demo: Things in Hierarchies (w/o RM/SQL)
http://www.garlic.com/~lynn/2004q.html#85 The TransRelational Model: Performance Concerns
http://www.garlic.com/~lynn/2005o.html#24 is a computer like an airport?
http://www.garlic.com/~lynn/2005p.html#8 EBCDIC to 6-bit and back
http://www.garlic.com/~lynn/2006o.html#18 RAMAC 305(?)