Re: In an RDBMS, what does "Data" mean?

In message <40ce4ecb$0$559$e4fe514c_at_news.xs4all.nl>, mAsterdam <mAsterdam_at_vrijdag.org> writes
>Anthony W. Youngman wrote:
>
>> mAsterdam writes
>>> Anthony W. Youngman wrote:
>>>
>>>> So if I put my data into an MV database I can access it as if it
>>>>were in an RDBMS. However, the converse is not true.
>>>
>>> It would be very interesting to know - in some detail -
>>> what kind of data gives difficulties in putting stuff
>>> from a RDBMS into a MV database.
>>> This maybe somewhat awkward in this newsgroup, because some
>>> will be just waiting to say: See? You *can* express proposition_set(x)
>>> in a RDBMS, and you *can't* in MV, therefore MV is better.
>>> More is not a priori better.
>>>
>>> But I trust you can stand that reaction. Could you give some examples?
>>>
>> Actually, all you have to do to make RDBMS appear (superficially) to
>>look like MV is to declare the appropriate views. This does, however,
>>have the unfortunate side-effect of presenting your application with
>>apparently redundant data.
>
>'superficially' only? explain.
>'unfortunate side-effect of presenting your application with
>apparently redundant data' what's so unfortunate in having
>redundancy in presenting stuff? This is getting to look more
>and more like sales-crap. I don't want to offend you, but
>please try to understand what I am asking instead of giving
>a rebuttal to a non-existent attack.
>

Sorry. I don't want to offend you either. But MV will present you with a normalised view of the data. If an RDBMS presents you with a view of the same data and it contains a "many" join, then the app will get multiple copies of certain bits of data. In relational, this could lead to an attempt to update one copy without realising that there IS only one copy, so all the others change as well. Yes that would be stupid programming, but an MV app would know that there was only one copy.

That's why I said "superficial". The MV app will know more about the data, because of the way the data is presented by the database.

Cheers,
Wol

-- 
Anthony W. Youngman - wol at thewolery dot demon dot co dot uk
HEX wondered how much he should tell the Wizards. He felt it would not be a
good idea to burden them with too much input. Hex always thought of his reports
as Lies-to-People.
The Science of Discworld : (c) Terry Pratchett 1999