Difficulty of DB refactoring was RE: [AM] [dm-discuss] ZZZ Farewell Fellow Agi

At 09:55 AM 2/2/2004 +0000, you wrote:

>It might be worth mentioning a fairly widely publicised, comparatively 
>recent change to data structures, just to illustrate the kind of thing 
>that DBAs have to take into account when they change a column.
>
>Remember Y2K?
>
>It is a fairly extreme example - we had to find and change a load of 
>columns, and then test everything. And have people standing by in case 
>anything got missed.
>
>But any change to a database has to be checked to see what else uses it - 
>other apps, interfaces, user reporting tools (Business Objects, Excel, 
>Access...) And if the DBA misses one, the project that asked for the 
>change probably won't get users phoning them up and screaming down the 
>phone... Which is one reason why they don't like changing columns 'on the fly'.

Yes, databases are often highly coupled to other things, such as apps, 
interfaces, ...  which I discuss at 
http://www.agiledata.org/essays/databaseRefactoring.html#WhyDatabaseRefactoringIsHard. 
What you need to do is reduce that coupling, by improving the design as 
well as by encapsulating access to your database.

You also need to introduce very good CM control (of your DDL, test data, 
reference data, ...) as well as regression tests for the both the database 
and everything that touches the database.



>Brief introduction (since this is my first post). I am a data architect, 
>been doing that for about 12 years now, mostly corporate/enterprise 
>architecture - which also involves being part of project teams and 
>providing either full data models or starter logical models so the 
>developers can get on and develop. Before I did this, I was a COBOL 
>analyst/programmer. I have been involved in four data warehouse projects - 
>two built, one abandoned when the company was sold, one may still be going 
>on as it was for the company that sold my then employers. I joined this 
>list to find out more about Agile methods, and see where Enterprise 
>Architecture fits in (I think I know, and when I am sure, I will post my 
>ideas).

Welcome to the list.  Looking forward to your posts.

- Scott

For more information about AM, visit the Agile Modeling Home Page at www.agilemodeling.com
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