Craig,
Wow - You stirred up some emotions with this question. I'm going to play
devil's advocate and say that I have seen instances where RI is not in the
database layer. It's probably more common in warehousing because you have
to load data even if some constraints are violated and then deal with them
later.
For example, if the General Ledger says $1,000 was transferred to Cost
Centre 1000 and we thought Cost Centre 1000 was closed we still need to
report the $1,000. Yes, it probably indicates a problem in the General
Ledger, but I've work in places where you just have to deal with it. These
problems tend to only occur in large organisations with hundreds of systems
and an unlucky data warehouse that's meant to join all the data back
together. Also from a performance point of view I have heard that it can
be faster to check say 1,000,000 rows for RI after loading, as opposed to 1
row at a time - someone with intimate knowledge or Oracle's RI
implementation may shoot me down on that suggestion though.
In your example though we're talking about a single OLTP system. Have I
seen an OLTP without RI - Yes. The system was an OO app with Oracle
implementing the persistent objects. Let's pretend it was for a City
Council, and there was a Payment object. Two of the attributes of the
Payment object are called PaymentIsForObject (describes an associated
object by name) and PaymentIsForKey (contains the key value of another
object). This other object though could be one of many things, perhaps
ParkingFine or LandTax or GarbageCollection. Therefore the RI of
PaymentIsForKey depends on the value of PaymentIsForObject. Again perhaps
someone can confirm if Oracle can do conditional RI like this, however at
the time I was lead to believe that it couldn't (I wasn't the DBA on this
project).
As others also mentioned - leaving RI out of the database still leaves a
pile of functionality available - complex queries, indexing, partitioning,
etc.
I do agree with the others though - Leaving RI out of the database probably
introduces a lot of risk but there may be a valid reason for doing so. On
the other hand, is they don't have a good reason for leaving it out then
put it in. Worst case, argue that it can be put in since their application
will make it redundant anyway - then as soon as the Oracle RI rejects a
record you can laugh in their face!
Please don't yell at me anybody - I just felt that I had to balance the
argument.
"Craig Healey"
<C.Healey@hhsu To: Multiple recipients of list ORACLE-L
<[EMAIL PROTECTED]>
k.com> cc:
Sent by: Subject: Theory v Practice
[EMAIL PROTECTED]
om
24/10/2002
03:45
Please respond
to ORACLE-L
The developers working on our new VB app are also responsible for
setting up the Oracle DB behind it. The app is for an order
entry/despatch/warehouse system with >5 million customers and >1000
orders per day. We have nearly 400 tables. They are not planning on
using primary keys/secondary keys, as they say they will handle all the
constraints via VB.
I only have a theoretical knowledge of database design, which says this
is very wrong. Is the Oracle system being used as anything more than an
expensive file system? In real world scenarios, is this a common
practice?
Regards
Craig Healey
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