Re: Reminder, blatant ad
From: Jan Hidders <jan.hidders_at_REMOVETHIS.pandora.be>
Date: Fri, 10 Feb 2006 23:18:43 GMT
Message-ID: <nb9Hf.248283$Og3.7667743_at_phobos.telenet-ops.be>
>>dawn wrote:
>>
>>>I'd like to better understand data independence in terms of
>>>functionality.
>>>
>>>Does it mean that if a new version of a DBMS tool takes the same
>>>logical specification it can lay the bytes down differently on the disk
>>>without application code changing?
>>
>>No.
>>
>>>Or does the decoupling of physical and logical mean that if I want to
>>>store attribute data physically "along with" a different entity (table)
>>>than where it is now (and rework the logical model), no application
>>>software needs to change?
>>
>>No.
>>
>>It means that you can make some changes in the physical model w/o having
>>to change the logical model. Note that this is different from what you
>>just said because you were talking about the logical model.
Date: Fri, 10 Feb 2006 23:18:43 GMT
Message-ID: <nb9Hf.248283$Og3.7667743_at_phobos.telenet-ops.be>
dawn wrote:
> Jan Hidders wrote: >
>>dawn wrote:
>>
>>>I'd like to better understand data independence in terms of
>>>functionality.
>>>
>>>Does it mean that if a new version of a DBMS tool takes the same
>>>logical specification it can lay the bytes down differently on the disk
>>>without application code changing?
>>
>>No.
>>
>>>Or does the decoupling of physical and logical mean that if I want to
>>>store attribute data physically "along with" a different entity (table)
>>>than where it is now (and rework the logical model), no application
>>>software needs to change?
>>
>>No.
>>
>>It means that you can make some changes in the physical model w/o having
>>to change the logical model. Note that this is different from what you
>>just said because you were talking about the logical model.
> > I thought that was what I was saying in the first answer. How is this > different?
The version of the DBMS tool doesn't change. You should be able to change the physical model w/o changing the tool.
>>>I'm likely confused on this topic as I have not studied it in depth.
>>
>>You probably should. It is the singlemost important notion for
>>understanding what the relational model is about.
> > It is likely because I have read a bit that I'm confused. Why would > you think that a change in the physical model of a non-relational DBMS > (e.g. PICK) would require reworking the logical model?
This is not necessarily true for all such systems but in many of those the logical and physical model are closely tied together and their efficiency in fact often depends on this close relationship.
- Jan Hidders