PSA tables are provided with a version if you make an incompatible change to the transfer structure (for example, change a length or delete fields).

When it is established, an incompatible change to the transfer structure has been made, a new version of the PSA, meaning a new PSA table, is created. Data is written to the new table when the next request is updated.

The original table remains unchanged and is given a version. For every request that was written in the old table, you can also continue to use all of the PSA tree functions.

The appropriate format is used for reading data from a PSA table.

• If the request was written to the PSA table before the change to the transfer structure, then the transfer structure format before the change is used.
• If the request was written to the PSA table after the change to the transfer structure, then the changed transfer structure format is used.