Re: Data independence

Alfredo Novoa wrote:
>>But suppose for example you have a table where the some two columns are
>>defined to be the primary key. Your application displays a window with
>>two fields for people to enter data.

> 
> You may have an application which reads the catalog tables and
> displays all the attributes.

Well such an application would be fine with schema changes. But typically you'd want your application to display a restricted set of columns.

>>Now you change the primary key to be some *three* columns. Or maybe two
>>totally different columns. It then becomes impossible to use the
>>application.

>
> You can use a default value for the hidden column.

But that would defeat the point of it being part of the primary key, if it is always the same value. Users might be required to enter a lot of data that requires this third column for uniqueness.

Let's take an absurd example: suppose I took away the whole database and replaced it with another entirely different database. Are you saying that applications should be able to carry on working fine? Clearly this isn't the case unless your application is totally general. In that case there's no need writing an application at all - just give users access to the standard admin GUI that comes with the DBMS.

Paul. Received on Mon May 17 2004 - 15:20:52 CEST