Re: The Foundation of OO (XDb)
Date: Mon, 17 Jun 2002 02:15:37 -0400
Message-ID: <P9fP8.537$a_5.82239626_at_radon.golden.net>
"Topmind" <topmind_at_technologist.com> wrote in message
news:MPG.17770c698480335698a5c6_at_news.earthlink.net...
> > Logically, a Video has a sequence of frames (pictures) and a stream of
sound
> > waves and everything necessary to synchronize them. Physically, though,
we
> > have many ways to represent Video. QuickTime, AVI and MPEG jump to mind.
> >
> > QuickTime, AVI and MPEG are not subtypes of Video; they are different
> > representations or encodings of the same type. Logically, they perform
the
> > same function perhaps with different performance and size
characteristics.
> >
> > Date's and Darwen's model of type allows the dbms to deliver all
possible
> > representations of Video at the logical level regardless of the actual
> > representation stored on the physical medium.
> >
> > Someone in the creative department querying the dbms might watch a Video
in
> > its QuickTime representation on their Mac. Someone it the engineering
> > department querying the same dbms might watch the same Video in its MPEG
> > representation on their unix workstation. Someone else might watch it as
an
> > AVI in Excel.
>
> FYI
>
> Here is one possible way to represent your scenario
What was wrong with the representation I gave? I like it a lot better than yours.
> Table: MediaItem
> --------------
> ProductionID
> RepresenationID
> Location (file name/path)
>
> Now, some DB's could allow the content to be in the table
> itself. However, if we don't want to assume that we
> have such support,
Why not assume user-defined type support? I assume it. I think that level of support for user-defined types is absolutely necessary. Why should we force users to deal with filenames? If these are relative path names, from what location are they relative? Does the user even have access to that directory? If they are absolute path names, how do we ensure all computers have that drive mapped to the same drive letter? How do we even know that the client computer uses drive letters? etc. etc. etc.
Besides, the actual representation is a strictly physical matter. Why make the user have to worry about it? Why make the system store all representations? Why not store a physical representation from which the dbms can derive all the others? Received on Mon Jun 17 2002 - 08:15:37 CEST