Re: best practice in upgrading db structure

Csaba Nagy wrote:

>[leaving the original text, as it is reply to an older posting]
>
>On Fri, 2006-03-31 at 21:26, Jim Nasby wrote:
>
>
>>On Mar 29, 2006, at 3:25 AM, Csaba Nagy wrote:
>>
>>
>>
>>>>Could somebody explain me, or point me to a resource where I can find
>>>>out what is the recommended practice when a live db needs to be
>>>>replaced
>>>>with a new version of it that has a slightly different structure?
>>>>
>>>>
>>>Our development infrastructure includes a development data base
>>>cluster,
>>>with one data base per developer, and a staging data base with a
>>>largish
>>>deployment of the current production data base version.
>>>
>>>The developers are free to test whatever data base modifications they
>>>need on their private development data base. We have a "setup_db"
>>>script, which creates the data base structure + initial data. The
>>>script
>>>is based on an XML file which is processed by XSLT to generate the
>>>actual schema for Oracle/Postgres. So the developers usually recreate
>>>
>>>
>>Have you considered releasing that creation code? I know there's lots
>>of places that have a need for stuff like this, and having used a
>>similar system before I know how powerful it can be. Unfortunately
>>the company I worked for was too paranoid to release the database
>>creation tool we used. :( Had they, maybe you wouldn't have had to
>>write one from scratch.
>>
>>
>
>I guess I still would have written it from scratch :-)
>
>There ARE some systems which do data mapping from/to code, but they all
>have problems: too generic, never exactly what you want, etc. What I did
>is: create a custom XML schema to describe the features I need from the
>DB, and a pair of XSL style sheets to translate that for
>postgres/oracle. I guess it would have been better to take another
>approach, i.e. write some templates (using some templating engine) and
>feed the data from the XML into that, but the result would be the same,
>if maybe a bit more readable...
>
>The conclusion is: if I would have to set up another system doing
>something similar, I would write it from scratch again. It really didn't
>take that much time, and it does exactly what I want.
>
>

Csaba, we made such a system the cornerstone of our entire toolchain.

I will ask, though, why use XML/XSL, why not use a format that lets you
load the data to tables, then you do a huge number of tricks with it
prior to generating the DDL, not the least of which is diff'ing current
structure to see what needs to be changed.

Anyway, our system uses a format that looks something like CSS, it is
documented here:

http://docs.secdat.com/index.php?gppn=Database+Specifications