Re: Generating tables with relationships in arc and part of primary key, bug?

reidlai_at_hk.super.net (Reid Lai) wrote:
>meldahl_at_pvv.unit.no (Ole Christian Meldahl) wrote:
 

>>I have three entites A, B and C. A relates to B and C with an arc and
>>(B,C)one-to-many(A). Both relationships are part of the UID of A.
 [...]
>>My actual problem relates to generation of tables from the entities.
 [...]
>>My conclusion is that the Generator/Wizard does not realize the
>>problem with arcs and primary keys.
 

>>If so, it's a bug! (IMHO, of course) The Wizard should have generated
>>an unique key instead.
 

>I think this is not a bug. In relational DBMS, referenced entities in
>a relationship must reference to the primary key of their referencing
>entities. For primary key definition, all composite key must be
>wholly null or wholly not null. Of course, the wholly null key means
>the key is non-exist.

Thanks for your help, but I think my problem-desription was a little confusing. Let me try with an example. And, btw, I meant that the bug was during generation of the tables, not necessariliy in the DBMS.

Lets say that table C are letters, table B are memos and table A are lines of text applying to both C and B. I need a definition such that I can store information like this:

Table C

Table B

Table A

lineno: 1 Letter_1 
lineno: 2 Letter_1 
lineno: 3 Letter_1 
lineno: 4 Letter_1 
lineno: 1 Letter_2 
lineno: 2 Letter_2
lineno: 1 Memo_1  
lineno: 1 Memo_2  
lineno: 2 Memo_2  
lineno: 3 Memo_2  

It is easy to model this with arcs, but the implementation...... (of course, the keys of B and C are different)

Hope this clarifies my problem!

Thanks again.

oli

--
Ole Christian Meldahl
"Sailor" 
Norwegian High Command, Information Systems
meldahl_at_pvv.unit.no