Long answer:
Where you may run into trouble is Unicode support in the Oracle 8i database. As part of your Xe -> 8.12 upgrade, you are forced to upgrade all schemas except Business Data and Control Tables to Unicode. Unicode support in 8i is not the same as Unicode support in 9.2/10.2; it is less of an implementation on 8i and you may have issues with certain data types.
"...national character set is specified as AL16UTF16 (the default setting for Oracle 9i). Because support for the UTF-16 character set was not introduced until Oracle 9i..." In other words, EnterpriseOne 8.9 introduced unicode support, and the upgrade guide requires the national character set to be specified as AL16UTF16. Kind of puts the damper on 8i...
If they don't already exist, create a dev and/or qa database with Oracle 8i. This is where you can test your database upgrade upon completion of the upgrade from OneWorld B7332 to Xe. If you currently have all schemas in one database, including production, copy the DEV/CRP/etc. schemas target database(s). This will help you to insulate production from upgrade activities. You can host multiple Oracle databases on the same host, with different versions (we do this), but ideally you would have separate hardware for upgrade sandbox and staging.
Once you're upgraded to OneWorld Xe, apply the latest stable SP23 Service Pack, and then upgrade the development database to 9.2/10.2.
*** I would not recommend Oracle 9.2 for most upgrades or installs, simply because Oracle recently moved the "sunset" date for support from summer 2007 (now) to summer 2008, ostensibly due to the release date of Database 11. This gives you less than a year to upgrade to 10.2 following your 8.12 upgrade. However, this is obviously your call.
Technically, but not ideally, and definitely not officially, the Deployment Server, Enterprise Server, JAS server & Client could possibly *connect* to an 8i database, provided Oracle client >=9.2 is installed on the DS/ES & Client, and you have >=9.2 JDBC on the JAS server. Oracle clients are backwards compatible with older versions of the database. Still, you will not be able to get support from Denver on this. Oracle DB 8i went over the sunset sometime in 2003 or early 2004. Then you must consider the Unicode issue, which could possibly prevent an upgrade all together.
Looking at an 8.96 ES, the libora80/libora81 files have been removed. This means you would be forced to install a db client >=9i Release 2 (9.0 is also not supported). JDE requires this library for OCI to the database. Be sure to select the correct driver in your JDE.INI on the Xe side. 8.9x no longer requires this setting, it will choose the correct driver based on the binaries in $ORACLE_HOME.
I must say I'm fascinated by some of the technical requirements I hear from project teams. If you don't mind my asking, what is the reason behind your desire to not upgrade the apps and database at the same time? I am also curious about your hardware...are you taking care of hardware upgrades, across the board, to take into account to larger memory footprint of the application and the conversion to Unicode? If not, talk to your hardware vendor for proper sizing.
