"So what's this thing here?" 

 

    The salesman smiled broadly.  "Well spotted!" he cried.  "I can see you're very observant."  I don't like car salesmen at the best of times.  "You'll really like this!  That's a top of the line function on this model; we call it the null control.  It stands for No Unpleasant Lifting or Logic.  It's a special feature." 

 

    "So what does it do?"  I wanted an automatic, with the two basic controls, brake and accelerator, which I like to think of as stop and go, respectively--nice and two-valued, in other words.  I'm a great believer in simple user interfaces.  "What does it do?" 

 

    "Oh, you're going to love this.  Trust me!  What does it do?  Well--imagine you're driving and you find yourself in some situation where normally you'd have to do some quick--but careful and accurate!--thinking ... or action ... or judgment ... or tact and finesse--anything like that.  Say the lights have just gone to amber, and you have to decide, quickly, whether to slow down or speed up.  Or the gate's beginning to come down at the railroad crossing, and a train's coming--same deal:  Do you slow down or speed up?  Or some junk has just fallen off a truck or something and appeared in front of you on the freeway:  Do you veer to the left or the right?  Or the gas gauge is on empty, and you don't know whether to drive a mile or two off the freeway to get gas or try to get home where you have some spare gas in a can.  EASY--all you do is hit the null control, and the system does the rest.  You don't have to think about it.  The null feature makes the decision for you and acts on it, instantly!" 

 

    "Hmmm ... I think I see.  But now you mention it, it seems to me I've heard about this thing before--in fact, I think I've heard some consumer advocates arguing against it.  What's going on, exactly?" 

 

    "Oh, you don't want to listen to those kooks.  All they're interested in is decrying all the latest technologies!  Look--do you think the SQL Motor Corporation would build and market a car that was unsafe?" 

 

    Oops.  He shouldn't have said that.  He knew it, too.  Unsafe?  A loaded word to inject into our conversation at this point!  "What do you mean, unsafe?" 

 

    "Oh, nothing ... nothing.  Nothing to worry about.  Nothing at all.  Look!  Look at all these other bright and shiny features!--real faux leatherette upholstery, five million radio channels, electronic sliding star roof, special circular bike rack ..."  He was on a roll now, but I interrupted him.  "No, no, no, wait a bit, wait a bit ... What do you mean, unsafe?" 

 

    "Well ..."--he looked a little shifty--"well, all right.  If you must.  I mean, if you really have to be pushy about it ..."  He stopped and looked over his shoulder.  "Look--come into my office a minute."  We moved off the showroom floor and into a small cubicle at the side, with a glass door.  He shut the door, rather carefully I thought, and pulled down the blind.  "Front desk--please hold all calls.  Thanks."  We sat down, and he turned to look at me. 

 

    "See, it's like this.  I wouldn't tell everyone this, but I like the look of you, see.  That null thing?  Well, it does do everything I said.  I mean, it's really great, you know!  In fact, it's just amazing!"  He began to wax enthusiastic again: Pavlovian reaction, I suppose.  Then he remembered what he was about.  "Yes, but ... The thing is, sometimes it just causes the most horrendous ... well, failures.  I mean ... er, that is ... I mean, what I'm trying to say is, sometimes you just ... Well, sometimes you just crash." 

 

    "WHAT?" 

 

    "Listen, I'm trying to tell you.  Most of the time that old null thing works just fine!  Usually you get away with it!  But, like I said, sometimes it just fails, dramatically ... and then you crash." 

 

    "I see."  I didn't know how to respond.  I mean, it was so unexpected!  After a few moments, I said:  "Can you tell when it's going to crash?  I mean, is there some warning?  Is there something that causes it?  Is there a way you can make sure it doesn't happen?" 

 

    He sighed, and for a moment--for a salesman--he looked almost haunted.  "No sir.  I don't know.  If I knew I'd tell you.  The fact is, it seems to be completely unpredictable.  Random."  He looked over his shoulder again.  He took a gulp from the glass of water sitting on his desk.  He seemed suddenly at a loss for words.  I felt I had to say something. 

 

    "OK.  Well, I suppose I have to thank you for making things so clear.  For being so honest, I mean."  He looked as if he was going to cry.  For a moment I almost felt sorry for him.  "But--well, you know, in the circumstances there's no way I'm going to buy this thing!  I mean:  Would you?  You'd have to be crazy!" 

 

    He heaved a deep sigh again.  "Yes, you're right.  OK, OK.  When you're right, you're right.  That's why we usually just don't mention the problem.  But you more or less forced me to ..."  He looked very unhappy.  "I wasn't always a car salesman, you know!  I used to have a respectable job.  I used to be a database application developer!  But then they sent my job overseas, and I was downsized out, and one thing led to another, and, well, here I am ... I still try to be as honest as the job will let me--I mean, I do my best--but sometimes it's really hard."  He pulled out a handkerchief and dabbed at his eyes for a moment.  "But ... I guess I should thank you.  You don't know what a relief this has been for me, to talk to you like this!  None of the other guys want to talk about it at all.  I don't think most of them even understand the problem, they just think that old null thing is so wonderful.  They're so ... oh, I don't know."  More than ever, I thought he was going to burst into tears. 

 

    "OK," I said, patting his arm.  "I won't tell anyone you've been honest.  Your reputation is safe with me.  But, like I say, I couldn't possibly buy this thing ... and in fact I feel obliged now to tell everyone else not to buy one, either!  The way I see it, even if I decided never to use that null thing myself, somebody else might drive my car and use it.  Right?  How could I stop that?  Hell, the only safe thing to do is never use it all, right?  It ought to be called the Never Use, Leave Alone control!  Why on earth would anybody design something like that?" 

 

    "Ah," he said, brightening again, "I can answer that one!"  I made an excuse and left.

 

 

Ed. Note: For a logically correct solution to missing data, without NULLs, see PRACTICAL DATABASE FOUNDATIONS paper #8, The Final NULL in the Coffin, by Fabian Pascal (this does not imply Date’s subscription to that solution).

 

 

Posted 12/10/04