Re: cdt glossary 0.1.1 [NULL]

mountain man quoted:
>> [NULL]
>> Roughly: a special marker that can be put in a place
>> inside a data structure where an actual value is expected.
>> Precisely what that marker means varies and there are at
>> least three possibilities that are sometimes assumed:
>>
>> (1) "Unknown value" This means that on the place of the marker
>> there should actually be a value but this value is not known
>> at the present time. For example, if a 'name' field in a tuple
>> describing a person is 'null' then this person will have a
>> name but we don't know it.
>>
>> (2) "Absent value" This means that the property that is
>> described by the value in question is simply not defined.
>> For example, if the 'shipping-date' field in a tuple
>> describing an order is 'null' then the order was
>> not shipped yet.
>>
>> (3) "Whatever SQL says it means" The exact meaning is hard to
>> summarize briefly, but is a mixture of the previous two
>> interpretations and involves a value with three truth-values
>> ('true', 'false' and 'unknown').
>>
>>
>> Common usage:
>>
>> - Confusion arises when people use terms like "null value",
>> a paradox to some, a contradictio in terminis to others.
>>
>> - Confusion arises due to the fact that nullness (the absence
>> of value) is often represented on computers by the number 0.
>> (Obviously, 0 is not null.)
>>
>> - In some contexts, 'null' and 'nil' mean the same thing;
>> in others, they do not.

> 
> Everything looks good to this point.
> But I cant understand the meaning of the
> following sentence ....
> 
> 

Could you elaborate? I really have difficulty seeing what might not be understood here - maybe the phrasing could be improved a little: "In the context of databases traditionally ..." ?

I prefer not to participate in opening this NULL can of worms again. NULL was discussed several times in c.d.t.; this is what came out. However, if subsequent discussion will lead to someone coming up with a better text (or better yet a reference) for the complete NULL entry, I'll be happy to copy & replace it.

> BTW, this FAQ has been greatly expanded since the last time
> I read it, and represents a valuable resource --- ONYA.
> Well done.

Thank you, on behalf of everybody who has contributed. (I don't remember exactly - but that includes you, no? -- not feeling like mining the archives right now)

What does ONYA stand for?
http://acronyms.thefreedictionary.com/ONYA says: "Oh No, You Again?" - I suspect I am missing a joke/subtlety for native English speakers here. Received on Sat Feb 10 2007 - 12:53:15 CET