Why relational algebra?

In the introduction, SQL sat just inside Datalog on the expressiveness spectrum. SQL’s engine is relational algebra: a handful of operations on whole tables.

A database has no variables and no rules, only tables and those operators. Translating Datalog into them pins down exactly what a program computes, in a language a database already runs. It is also how Datamog’s SQL backends evaluate your rules.

The punchline, built up over the next slides: non-recursive Datalog is relational algebra, and recursion adds one thing more, a least fixed point.