I picked up a small comment from Hannes Papenberg from the Joomla 1.6 development team some time ago. He was talking about the process of upgrading from Joomla 1.5 to 1.6.
Today, Joomla is upgraded by copying all the files for the upgrade into the web root of the site. This works fine, and there are also some upgrade scripts that makes this process even faster.
Upgrading to a completely new version of Joomla is another case. Joomla 1.6 will have a lot of new functions and changes. Not only the files will change but also the structure of the tables, and some files will be deleted. Those things don't happen in a regular upgrade. Thus, the upgrade process is not just about copying files. Normally, the process would be to delete all of the files for 1.5, and then migrate all data, image files and setup into Joomla 1.6 manually. This is not ideal. For this reason, Hannes from the development team has proposed that a migration script be made.
I would prefer that people would not have to delete all their files, install 1.6 and then migrate data over from 1.5. My dream for the update process from 1.5 to 1.6 would be an updater-component. That component would ship with all the files from 1.6 and after installation, you just select it from the component menu and it starts the update process. So it has to move around a lot of files, delete the obsolete ones and do table updates. This will trigger the max_execution limit, so this has to happen with a bunch of ajax requests and several page loads. But that's just me dreaming. ;-)
Later, Airton Torres answers with the following:
...it won't be necessary a migration script like we had from 1.0 to 1.5. No need for a new 1.6 site to migrate the old 1.5 site's database.
We will need a script that will take care of the changes in the tables an Pd also of deleting the files that will need to be deleted.
As you understand, whatever method for upgrading Joomla we end up with, it seems to me like the development team has a plan. I look forward to seeing the finished solution - a upgrade script would save a lot of time for me. I've got quite a lot of sites to upgrade when the time comes for the Joomla 1.6 upgrade.
• Read the post: Matias Aguirre needs help finishing Joomla! 1.5 to 1.6 migrator [Interview]
• There is also a Wiki page on Joomla 1.5 to 1.6 migration over at joomla.org.
You can read the original discussion here.