Re: Migrating from Hierarchial DB model to RDBMS OR ?
Date: Wed, 18 May 2016 20:16:26 -0400
Message-Id: <20160518201626.3efd9c4214738cf2b4f7ffa5_at_speakeasy.net>
On Mon, 16 May 2016 13:17:05 -0700 (PDT)
vldm10 <vldm10_at_yahoo.com> wrote:
> > Please note XML is Hierarchial as well but not sure how different
I doubt it. You say serious; I say chimera.
> This topic has the following name: Mapping one data model into another
No general transformation is possible. Any data can be modelled
relationally. That they have some hierchical representation just
provides a starting point.
As it happens I've had cause lately to investigate IMS. c.d.t readers
might not know how little it resembles a SQL DBMS:
> > it is from IMS
>
>
> I would like to mention that this post is one of the most serious
> issues and problems in DB theory.
> data model.
>
> Related to this problem, I gave my solution for this problem.
Any comparison to the relational model is purely specious. It is not a model. It lacks a basic datatype (analogous to relations), an algebra, and constraint enforcement.
Why would anyone use it, then? How is it IBM continues to sell IMS?
There still exist applications for which the services and features provided by SQL are not needed. If you have a record-keeping system for which the requirements are quite static and the data volumes very high, what need is there for predicate enforcement in the DBMS? If the rules are already enforced and the access patterns already established, why incur the overhead of dynamic storage allocation and location independence? Why "interpret a query" when you can just fetch a record by its key?
These are two different systems. Codd recognized that the power of mathematics would make database management more tractable and rational. He understood that not all data processing need be pure record-keeping. He invented an alternative, and was proved right. But the thing he invented was utterly, completely different. Any comparison risks pure sophistry.
--jkl Received on Thu May 19 2016 - 02:16:26 CEST