I agree with Jack on the relational part. Relational models can be implemented un SAS. Database functionality to support the integrity of relational models exist in Base SAS, not in SPDE/SPDS.
What I think is not fully implemented in SAS is MS part of RDBMS, which means integrated user management, storage management, logging, change tracking etc. So I think when building mission critical systems, one tend to look for other storage solutions than SAS.
/Linus
Data never sleeps