Re: cdt glossary - TABLE

mAsterdam wrote:
> Jan Hidders wrote:

>>
>> Yeah, I think we could be a bit more explicit here. It would say 
>> something like:
>>
>> A *table* consists of a table header and a body. The *table header* 
>> consists of a list of column names that contains each column name at 
>> most once and associates with each column name in that list a certain 
>> type. The *body* is a bag of rows where a *row* is a list of values 
>> that conforms to the table header.

No, that follows form the fact that all the rows have to be conform to the header.

> Just the "unorderedness" of bag is crucial here, right?

Yes.

> Another thing bugging me is: every representation of
> a table /has/ order - but the tables we speak about
> have none - or do we pretend they have none?

That's the same, really. :-)

> I would apreciate it if we would have a friendly explanation
> for that - it confuses anyone when starting to think about
> tables at first.

Here goes:

Note that a representation of a table in memory or on paper will always necessarily introduce an order on the elements. This is similar to how denotations of a set such as {a, b, c} and {c, b, a} also introduce each a different order on the elements of the set. In the first denotation the order is a < b < c, in the second it is c < b < a. This order, however, is merely an aspect of the representation and not a property of the thing that is represented. In other words, the two different denotations actually represent the same thing. For tables this means that the order in memory of the representation of the body is not really part of the body, or, put in another way, if we change that order in the representation then it would still represent the same body.

Hmmm, perhaps I'm still being a bit too abstract here. Perhaps you can improve?

• Jan Hidders