“Split schema” refers to the idea of classifying the database tables used by PegaRULES into two categories: rules tables and data tables. The primary goal for this is to decrease the amount of time a system must be unavailable during an upgrade. As such, this epic is a key part of the “high availability” goal.
The principle behind this idea is that rules change significantly from one release to the next, whereas data and work transcend releases. During an upgrade, one would install a completely new set of rules tables, while keeping the data tables (essentially) untouched. The system would be up and running during this time. Once the system administrator is ready to “pull the trigger” and start using the new version he can then update the PegaRULES table mappings to point to the new rules schema. This last step would require some downtime; but not as nearly as much as upgrades do today, when the system needs to be down during the whole upgrade process.