Consider the following relational database schema:
- EMP (eno name, age)
- PROJ (pno name)
- INVOLVED (eno, pno)
EMP contains information about employees. PROJ about projects and involved about which employees involved in which projects. The underlined attributes are the primary keys for the respective relations.
State in English (in not more than 15 words)
What the following relational algebra expressions are designed to determine
-
$\Pi_{eno}(\text{INVOLVED}) - \Pi_{eno} ((\Pi_{eno}(\text{INVOLVED}) \times \Pi_{pno}(\text{PROJ}))-\text{INVOLVED})$
-
$\Pi_{age}(\text{EMP})-\Pi_{age} (\sigma _{ E.age<Emp.age}( (\rho E(\text{EMP}) \times \text{EMP})) $
(Note: $\rho E(\text{EMP}) $ conceptually makes a copy of $\text{EMP}$ and names it $E$ ($\rho$ is called the rename operator))