Re: Pizza Example

"Tony" <andrewst_at_onetel.net.uk> wrote in message news:c0e3f26e.0404041156.ae57634_at_posting.google.com... > "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message news:<c4p4q7$on1$1_at_news.netins.net>...
> > "Tony" <andrewst_at_onetel.net.uk> wrote in message
> > news:c0e3f26e.0404040326.7e59f8f9_at_posting.google.com...
> > > "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
> > news:<c4o2at$frb$1_at_news.netins.net>...
> > > > "rkc" <rkc_at_yabba.dabba.do.rochester.rr.bomb> wrote in message
> > > > news:QtLbc.26194$nr4.17312_at_twister.nyroc.rr.com...
> > > > >
> > > > > "Dawn M. Wolthuis" <dwolt_at_tincat-group.com> wrote in message
> > > > > news:c4nglq$7pt$1_at_news.netins.net...
> > <snip>

>
> SQL DBMSs, not RDBMSs as such.  But I didn't have to do that.   I
> could use e.g. Oracle's CLOB datatype, which allows up to 4GB of data.
>  Or I could have said varchar2(4000).  RDBMS designers tend to like to
> impose some kind of discipline on the data being stored, it isn't
> really a performance issue - at least not from the DBMS's point of
> view.  But if you allow 4000 character pizza names in the database,
> then you must allow for that in your user interface, which means
> declaring 4000-character variables - something of a memory drain,
> perhaps?  Frankly it would just seem rather stupid to allow unlimited
> length for every data item.

I see no logic in this. The database need not constrain the size of data that is stored and the UI can either constrain it or not, as the designer/user see fit. Constraining the database to only store up to a particular length means that the database needs to be changed if a new valid value for an attribute arises that is longer than what was anticipated. The UI can permit scrolling to show only a limited number of characters, but scroll to show all. A report writer can wrap long values to a certain width for practicality. Unless there is a REAL business reason for limiting the number of characters for a value (or your DBMS product requires it or gives you better features if you do), don't do it. From what I have seen of RDBMS tools, those who use them are inclined to put an attribute of "color" in the database (for example) with a max number of characters for the value. All we need, then, is a new color to come available and you can bet that the name will be abbreviated now to keep it within that length. How silly IMO.

> > So, now, if you don't make the assumption that every item that someone
could
> > buy would have each attribute (such as Sauce), then how would you do
> > t? --dawn

>
> In a SQL database you could just allow NULLs in those items.  In a
> true RDBMS that doesn't allow nulls you could either create a table
> for each subtype of order_items or you could move the attributes like
> crust_name into separate tables like:
>
> create table order_item_crust
> ( order_no integer, item_no integer, crust_name references crusts
> , foreign key (order_no, item_no) references pizza_order_items
> , primary key (order_no, item_no)
> );
>
> (Note that this table only allows a maximum of one crust per pizza).

Yes, this does look like an RDBMS approach to the problem. I don't think it is a "natural" way to view the problem, but it follows a set of rules for what that is worth.
smiles. --dawn Received on Sun Apr 04 2004 - 22:28:25 CEST