The DML (data manipulation language) is how you interact with the database under a data model (46:07).
Two categories
| Category | Meaning | Basis |
|---|---|---|
| Procedural | You specify the exact steps the DBMS must execute — effectively writing the query plan yourself | Relational algebra (46:07, 46:39) |
| Non-procedural / declarative | You specify the answer you want, not how to compute it | Relational calculus (46:39, 47:05) |
Practical notes
- No DBMS exposes a relational algebra interface — it is too cumbersome to write by hand, and it forces you to define the query plan (
46:39). - Most systems support a declarative language instead (SQL) (
47:05). - Relational calculus is not required for this course. It surfaces in the advanced/query-optimizer classes. Earlier versions of the course taught it, but nobody uses it in practice unless writing query optimizers (
47:05,47:30). - The lecture focuses on relational algebra because it is the procedural foundation the query engine is built on (
46:39).