Hi,
CA PPM data structure is defined by following Entity Relationship Diagrams(ERD).
I hope it is useful for your investigation.
https://docops.ca.com/ca-ppm/15-3/en/reference/ca-ppm-entity-relationship-diagrams-erd
PPM requires Relational Database to implement above ERD. (Oracle and SQL Server are supported Database currently)
I cannot imagine that PPM does not use Relational Database.
Because if PPM uses flat files, I believe that critical performance issue will occur and it will be very hard to keep data integrity.
Thank you.