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Re: Database design problem - resolving many-many relationships

From: Ramani <vrhash_at_yahoo.com>
Date: 23 May 2002 11:15:15 -0700
Message-ID: <d49237dd.0205231015.2997317b@posting.google.com>


...
Lennart, Thanks for your response!!I now know where I stand..Here is something more..
The table struct for the hard_disk
hard_disk (disk_id primary key

           capacity)
The hard_disk table contains just 1 attribute - the capacity; and since this is unique, this could be the primary key too. There are no other attributes like the type, make etc. Can I change it into:
hard_disk ( capacity varchar(20) primary key)

The same goes for the hardware MAC address of each computer. The Mac addresses are unique and hence I can just make a table with 1 column - the MAC address.
network_addr (mac_addr varchar(30) primary key)                

Is this a good design - A table containing just the primary key?? Thanks again!

lennart_at_kommunicera.umea.se (Lennart Jonsson) wrote in message news:<6dae7e65.0205221930.7bb712ea_at_posting.google.com>...  

> > Now, what i've thought of is to resolve the many -many relations by
> > creating a table for the relations.
> > The part I am most confused about is the hard drives and Network
> > addresses.A comp may or may not have more than 1 hard disk. Same goes
> > forthe Network addresses. So, it make sense to create a separate table
> > for the relation -
> > in the case of hard disc and Network addresses..
> >
> > comp_hard_disk( comp_id foreign key references comp_details
> > hard_disk_id foreign key references hard_disk)
> >
> > comp_network_addr( comp_id foreign key references comp_details
> > addr_id foreign key references network_addr)
> >
>
> I would say that this is the way to go.
>
> >
> > This would be too tiresome since I have almost 600-700 comps to deal
> > with.
> > Also, the no. of addresses will run into thousands.
>
> I'm not sure I follow, what is the problem with a couple of thousand
> things?
>
> > Should I just go ahead and create 2 columns for hard disks in
> > comp_details table as Hard_disk_1 and hard_disk_2 and create 4 columns
> > for addr as mac_1, mac_2, mac_3, ip ?
> > This violates the normalization rules..
>
> If you had a fixed amount of for example addr, then perhaps. Otherwise
> I would advise not to. Consider for example the number of OS you can
> run on a standard PC
>
> RH, Suse, FreeBSD, Win, OS/2, etc (not to mention different
> versions)
>
> I you make room for x nr. of os, I'll bet there will be x+1 nr. of os
> on some pc within polynomial time :-)
>
>
> /Lennart
Received on Thu May 23 2002 - 13:15:15 CDT

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