Question

3. Using the INVOICE table structure shown in Table P6.3, do the following:

Table P6.3

a.   Write the relational schema, draw its dependency diagram, and identify all dependencies, including all partial and transitive dependencies. You can assume that the table does not contain repeating groups and that an invoice number references more than one product. (Hint: This table uses a composite primary key.)

b.   Remove all partial dependencies, write the relational schema, and draw the new dependency diagrams. Identify the normal forms for each table structure you created.

NOTE You can assume that any given product is supplied by a single vendor, but a vendor can supply many products. Therefore, it is proper to conclude that the following dependency exists:

PROD_NUM → PROD_LABEL, PROD_PRICE, VEND_CODE, VEND_NAME

(Hint: Your actions should produce three dependency diagrams.)

c.   Remove all transitive dependencies, write the relational schema, and draw the new dependency diagrams. Also identify the normal forms for each table structure you created.”

Answer 1

3a.

Identify that (INV_NUM, PROD_NUM) as primary key, because, using this pair any row in the table can be uniquely identified.

Identify the following dependencies:

Desirable dependencies:

(INV_NUM,PROD_NUM) → SALE_DATE,PROD_LABEL,VEND_CODE,VEND_NAME,QUANT_SOLD,PROD_PRICE

Partial dependencies:

INV_NUM → SALE_DATE

PROD_NUM → PROD_DESCRIPTION, VEND_CODE, VEND_NAME, PROD_PRICE

Transitive dependency:

PROD_NUM→VEND_NAME (i.e. PROD_NUM→VEND_CODE, VEND_CODE→ VEND_NAME)

3.b

To remove partial dependencies, create new tables as follows:

R2: (INV_NUM, SALE_DATE) - 3NF

R3: (PROD_NUM, PROD_DESCRIPTION, VEND_CODE, VEND_NAME, PROD_PRICE)-2NF

R3 have no partial dependencies. Therefore R3 is said to be 2NF. But, R3 is not 3NF, because, R3 still have transitive dependencies.

R4: (INV_NUM, PROD_NUM, QUANT_SOLD)-3NF

R2 and R4 are said to be 3NF, because R2 and R4 has not partial or transitive dependencies

3.c

To remove transitive dependencies, each transitive dependency into two tables as follows:

R5: (PROD_NUM, PROD_DESCRIPTION, VEND_CODE, PROD_PRICE) -3NF

R6: (VEND_CODE, VEND_NAME)-3NF