Editing Upgrading EPM Packages (section)

=Upgrade Methodology=

When an upgrade is done performed upon a package the '''postinst method is not called''' rather an '''upgrade''' method is called and passed the two version numbers. These version numbers correspond to the old version being upgraded and the new version being installed respectively. 

==Files on Disk Upgrade==
This is the first stage of any upgrade.

* Any files belonging to the old version are removed or replaced by new versions. 
* Any new files which were not there before are added.
* Any errors (e.g. files not under package management cos they have changed) results in an error and the old files are put back and the upgrade aborts. 

==API Calls==
These would have been performed initially by the POSTINST method. However neither this nor the PRERM method are called during an upgrade. Any changes required between versions must be defined in the upgrade method. 

==Data and Datasets==
Datasets are defined in config files, thus any dataset changes are applied. 

No data is lost unless the field containing that data is no longer defined by any config file. 

Interactive Install/Upgrade/Remove will allow the users to change this behaviour and keep the data even if it actually becomes inaccessible due to nothing in EPrints understanding it.