Click here to monitor SSC
SQLServerCentral is supported by Red Gate Software Ltd.
 
Log in  ::  Register  ::  Not logged in
 
 
 
        
Home       Members    Calendar    Who's On


Add to briefcase ««12

Codd's Rules Expand / Collapse
Author
Message
Posted Thursday, December 11, 2003 6:08 PM
SSC Eights!

SSC Eights!SSC Eights!SSC Eights!SSC Eights!SSC Eights!SSC Eights!SSC Eights!SSC Eights!

Group: General Forum Members
Last Login: Tuesday, July 31, 2007 8:20 AM
Points: 885, Visits: 1
Hi Frank

I hear you loud and clear :)

Thanks for the article btw, I actually did enjoy it along with your others... I have a real admiration of Codd et al and true, there is a fair number of rules missed by designers and dba's alike that have been long since proven but often ignored.

Best Regards

Ck



Chris Kempster
www.chriskempster.com
Author of "SQL Server 2k for the Oracle DBA"



Chris Kempster
www.chriskempster.com
Author of "SQL Server Backup, Recovery & Troubleshooting"
Author of "SQL Server 2k for the Oracle DBA"
Post #89054
Posted Friday, December 12, 2003 2:02 AM


SSCertifiable

SSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiable

Group: General Forum Members
Last Login: Tuesday, August 13, 2013 1:18 AM
Points: 5,956, Visits: 285
Hi Chris,

glad to see, you didn't get me wrong !!!!

Let me give an realworld example.
At the beginning of last year my company decided we need a system to manage our mutual funds, because our unit-linked products grow both in size and importance.
Now, because I live in both worlds, I said ok, I will do this.
Our management was concerned what might happen when I leave the company, who will be there to care for the system, who will know what the system does....
So they decided to give this to a third party software company. The requirements were SQL Server as DBMS and VB6 as programming language (I wouldn't have done anything else, btw).
Then, the programmer arrived and stayed two weeks with us to get the idea what we want and what functionality this system needs to have.
Now, this programmer was
- not familiar with SQL Server (first project with this DBMS)
- not familiar with VB (first project with VB)
- had no clue about overall treatment of assets like book-keeping and alike

I had to do that much overtime to explain our requirements to him, that I would have been far better off doing this by myself.
Now one and a half year later, the system is in production and it is close to collapse. There is that much garbage in that db, the general responding times are unacceptable and overall performance is poor.
Management realized this and now guess whom they ask to look at bugs???

After all, this funny exercise was at a cost of some 60k Euros.

Frank
http://www.insidesql.de
http://www.familienzirkus.de


--
Frank Kalis
Microsoft SQL Server MVP
Webmaster: http://www.insidesql.org/blogs
My blog: http://www.insidesql.org/blogs/frankkalis/
Post #89055
Posted Sunday, December 14, 2003 8:47 PM
Valued Member

Valued MemberValued MemberValued MemberValued MemberValued MemberValued MemberValued MemberValued Member

Group: General Forum Members
Last Login: Thursday, May 21, 2009 5:23 PM
Points: 70, Visits: 5
It is good to be reminded just what RELATIONAL means.

XML is an example. Your piece of XML will itself have columns and rows, so it is logically a table (relation). By wrapping it up as a string and storing it in a column, you are logically nesting tables.

You database engine may allow you to step outside the bounds of relational principles this way, but the price you pay is that nicely interchangable tools that have developed due to the consistency of the relational model, like report writers for example, will not work with such arbitrary models. Not that XML itself cannot be recognised as relational data, its where its usage breaks the rules, such as nesting tables.

XML in particular is better thought of as a TRANSPORT for relational data, and as such you want translators to/from XML and native tabular protocols. I think SQLServer got it wrong. Instead of SELECT..FOR XML, there should have been an alternative type of CONNECTION that used XML as the transport, and every SQL statement should be independent of which type of transport it will use. In ADO, XML would be a subclass of Recordset. I hate to think that all the stored procedures that existed on one database I worked on, would all need to be cloned for an XML version.



Post #89056
Posted Monday, December 15, 2003 1:33 AM


SSCertifiable

SSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiable

Group: General Forum Members
Last Login: Tuesday, August 13, 2013 1:18 AM
Points: 5,956, Visits: 285
I totally agree. It's good to remember and even better to learn what RELATIONAL means.

Just a while ago we had some interesting discussions on pros and cons of XML.
I'm not going to argue here on XML.

Frank
http://www.insidesql.de
http://www.familienzirkus.de


--
Frank Kalis
Microsoft SQL Server MVP
Webmaster: http://www.insidesql.org/blogs
My blog: http://www.insidesql.org/blogs/frankkalis/
Post #89057
Posted Friday, January 28, 2011 4:02 PM


SSCertifiable

SSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiableSSCertifiable

Group: General Forum Members
Last Login: Today @ 9:35 AM
Points: 7,874, Visits: 9,613
Frank Kalis, article
Updateable views are not always possible. For example there is a problem when a view addresses only that part of a table that includes no candidate key. This could mean that updates could cause entity integrity violations. Some sources on the internet state that 'Codd himself did not fully understand this'. I haven't found any rationale for this.

I know it's more than 7 years on, but the article raises a particular question/issue that has not been resolved in the comments so far so thios comment, although very late, may still be useful.

I think that the thing that people (including Codd himself) didn't understand (in 1985: he did understand it later) in respect of updateable views wasn't that not all views were updateable (he certainly understood that, else he would not have talked about theoretically updateable views) but that there is no effectively computable algorithm which is guaranteed, given a view definition and the definitions of the underlying tables (assumed to be in 5NF, using NF definitions which allow non-key columns to be nullable - as did all the original definitions), to terminate after finite time and indicate whether the view is theoretically updateable or not. He mentions this in the RM 2 book you reference (the solution was to have some algorithms that were pessimistic - sometimes they would say something was not updateable when it was, but they were guaranteed always to terminate) and chage the updateable view requirement to say only that views updateable according to whatever algorithm the system used would be updateable instead of saying that all theoretically updateable views would be updateable - the trade-off here was that this slight loss of generality for view updateableness made the rule possible to implement (or another way of looking at it was that he introduced a meta-rule that all the rules had to be effectively computable, and this forced a change in the view update rule).

The lack of an effectively computable algorithm to decide view updateability was not discovered until after the two 1985 articles had been published, so Codd's failure to recognise that issue is not in any way remarkable or surprising, nor does it indicate any kind of careless or failure of competence on Codd's part. He did of course recognise the issue with his updatability rule as soon as this lack was discovered and he was informed of it.


Tom
Post #1055675
« Prev Topic | Next Topic »

Add to briefcase ««12

Permissions Expand / Collapse