Boolean variables can be assigned either directly by using values TRUE, FALSE, or NULL or as the results of logical expressions : Boolean « PL SQL Data Types « Oracle PL/SQL Tutorial

1. Oracle PL/SQL Tutorial
2. PL SQL Data Types
3. Boolean

SQL>
SQL>
SQL> declare
  2      v_b BOOLEAN:=false;
  3  begin
  4      v_b:=extract(year from sysdate)>2000;
  5      if v_b then
  6          DBMS_OUTPUT.put_line('21st Century!');
  7      end if;
  8  end;
  9  /
21st Century!

PL/SQL procedure successfully completed.

SQL>