2. Primary Key Constraint: Answer in keywords (in bullet points or keywords for each question) 2-1) What is Primary key and Entity Constraint? Hint: List two rules for the valid primary key values to be inserted/updated. 2-2) What are two required properties to be qualified as a key (PK)? Hint: List two rules to be qualified as a key when choosing PK. 2-3) What does the DDL code PRIMARY KEY (ssn) as in the DDL of Person Table? Hint: Answer briefly what does your RDBMS Server do when a table is created with PRIMARY KEY (ssn) in the table definition as seen in Person table? (Answer in one brief sentence or a bullet point) 3. Referential Integrity Constraint: Answer in bullet points or keywords for each question 3-1) What is Referential Integrity Constraint in RDBMS? Hint: Specify the rules (in general) for the valid Foreign Key column values of a table to be inserted/updated 3-2) What does the DDL Clause Foreign Key (Dno) References Department (Dnumber) do as in the DDL for the table Person? Hint: What your RDBMS server would do for the FK column values to be inserted if Dno is declared as FK referencing PK Dnumber of Department table. Answer briefly in one sentence with the example department table below. Assume that the table Department is already populated successfully with the valid PK Dnumber values as follow: DEPARTMENT DNAME Headquarters Administration Research Automation DNUMBER 1 4 5 7 MGRSSN 888665555 987654321 333445555 123456789 MGRSTARTDATE 19-Jun-71 01-Jan-85 22-May-78 06-Oct-05