Re: cdt glossary - TABLE

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 10 Jul 2005 15:21:22 +0200
Message-ID: <42d120d5$0$8315$e4fe514c@news.xs4all.nl>

Paul wrote:
> mAsterdam wrote:
>

>>>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.
>>
>>The bag you speak of is not a mixed bag.
>>Just the "unorderedness" of bag is crucial here, right?
>>
>>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?
>>I would apreciate it if we would have a friendly explanation
>>for that - it confuses anyone when starting to think about
>>tables at first.

>
>
> You could say the table header is an (unordered) set of column names.
>
> And the rows are (unordered) sets of (column_name, value) tuples such
> that there is the obvious 1-1 mapping between the members of each row
> and the table header.
>
> I think I've seen this description somewhere and it gets round the
> problem of column order. Though possibly it makes the description more
> complicated for newbies.

Lists are ordered by definition
(http://en.wikipedia.org/wiki/List), so

        "the table header is an (unordered) set of column names"

directly contradicts

        "the table header consists of a list of column names"

I don't have a problem listing contradictory definitions if they are in use somewhere (in database context). However, this is the first time I see a table header with *un*ordered column names mentioned. Are you sure? Could you provide some background? Received on Sun Jul 10 2005 - 08:21:22 CDT