Re:Why Not to Build a Time-Series Database
by manigandham on Thursday November 08, 2018 @12:04PM
(#18407757)
Why does it matter what it was originally? We're talking about what the product is today, not 20 years ago.
kdb+ supports a superset of SQL and relational algebra, so it's a relational database. How it's implemented doesn't matter if it provide the functionality, which it can.
The definition of relational is very precise, whether you use the domain calculus, relational calculus or relational algebra. Wiki has a good summary of what must be natively supported by a database system to be relational: https://en.wikipedia.org/wiki/Relational_algebra
If you don't implement this at the transaction log level, but implement it via emulation at the output level, you can't make full relational guarantees, so these operations are fundamental to database design.