INF2603/202/2/2019
Tutorial letter 202/2/2019
Databases 1
INF2603
Semester 2
ASSIGNMENT 02 Marking Rubric/Guide
School of Computing
IMPORTANT INFORMATION:
This tutorial letter contains important information
about your module.
Marking Guide of Assignment 02 S2
TOTAL MARKS: 100
Due date
Tutorial matter covered in prescribed book
20 September 2019
All chapters in the syllabus (Chapter 1 to 8)
Unique number: 842182
Question 1
[18]
1.1. What is a subtype discriminator? Given an example of its use.
(3)
1.2. Under what circumstances are composite primary keys appropriate?
(4)
1.3. What are time-variant data, and how would you deal with such data from a database design
point of view?
1.4. Why are entity integrity and referential integrity important in a database?
(2)
(2)
1.5. What two conditions must be met before an entity can be classified as a weak entity? Give
an example of a weak entity.
(3)
1.6. Briefly, but precisely, explain the difference between single-valued attributes and simple
attributes. Give an example of each.
(4)
ANSWER
1.1. What is a subtype discriminator? Given an example of its use.
(3)
Read section 5-1d on page 172, 2 marks for description and 1 mark for giving example
1.2. Under what circumstances are composite primary keys appropriate?
(4)
Read on page 177-179 (4 marks for discussing two cases to the fullest)
1.3. What are time-variant data, and how would you deal with such data from a database design
point of view?
(2)
Read section 5-4b on page 182 (1 mark for defining time-variant data and 1 mark for
explaining how to deal with data that changes over times from a database design point of
view).
1.4. Why are entity integrity and referential integrity important in a database?
Solution
2
(2)
INF2603/202
Entity integrity and referential integrity are important because they are the basis for expressing and
implementing relationships in the entity relationship model. Entity integrity ensures that each row is
uniquely identified by the primary key. Therefore, entity integrity means that a proper search for an
existing tuple (row) will always be successful. (And the failure to find a match on a row search will
always mean that the row for which the search is conducted does not exist in that table.) Referential
integrity means that, if the foreign key contains a value, that value refers to an existing valid tuple
(row) in another relation. Therefore, referential integrity ensures that it will be impossible to assign a
non-existing foreign key value to a table.
1.5. What two conditions must be met before an entity can be classified as a weak entity? Give
an example of a weak entity.
(3)
Read section 4-1g on page 125, 2 marks for discussing 2 classifications, and 1 mark for
giving example (page 126-7)
1.6. Briefly, but precisely, explain the difference between single-valued attributes and simple
attributes. Give an example of each.
(4)
Read section 4-1b about attributes on page 117, 2 marks for explanation and 1 mark for
each example.
Question 2
[10]
Suppose you are working within the framework of the conceptual model shown in ERD diagram
below.
The ERD FIGURE
a. Write the business rules reflected in this ERD.
3
ANSWER:
Learn more about business rules in sections 2-3 and 2-4. The figure has 6 entities and 5 relationships.
Please note that there are optional and mandatory entities. In your answer, each relationship in both
directions must produce 2 business rules (1 mark for each). Read about the application of business
rules throughout the book. Also know how to differentiate 1:M 0r 1..*, M:N or *..* and 1:1 or 1..1
relationships.
Question 3
[46]
Suppose that you have been given the table structure and data shown in Table 3.1, which was
imported from an Excel spreadsheet. The data reflect that a professor can have multiple advisees, can
serve on multiple committees, and can edit more than one journal.
Table 3.1: Sample PROFESSOR Records
Attribute Name
Sample Value
Sample Value
Sample Value
EMP_NUM
PROF_RANK
EMP_NAME
DEPT_CODE
DEPT_NAME
123
Professor
Ghee
CIS
Computer Info.
Systems
KDD-567
1215, 2312, 3233,
2218, 2098
104
Asst. Professor
Rankin
CHEM
Chemistry
118
Assoc. Professor
Ortega
CIS
Computer Info.
Systems
KDD-562
2134, 2789, 3456,
2002, 2046, 2018,
2764
PROF_OFFICE
ADVISEE
COMMITTEE_CODE
JOURNAL_CODE
PROMO, TRAF
APPL, DEV
JMIS, QED,
JMGT
BLF-119
3102, 2782, 3311,
2008, 2876, 2222,
3745, 1783,
2378
DEV
SPR, TRAF
Sample Value
Assoc. Professor
Smith
ENG
English
PRT-345
2873, 2765, 2238,
2901, 2308
PROMO, SPR
DEV
JCIS, JMGT
Given the information in Table:
a.
Draw the dependency diagram.
(6)
b.
Identify the multivalued dependencies.
(3)
c.
Create the dependency diagrams to yield a set of table structures in 3NF.
(4)
d.
Eliminate the multivalued dependencies by converting the affected table structures to 4NF.(7)
e.
Draw the Crow’s Foot ERD to reflect the dependency diagrams you drew in Part c. (Note: You
might have to create additional attributes to define the proper PKs and FKs. Make sure that all of
your attributes conform to the naming conventions.)
(26) [8,4,7,7]
ANSWERS:
Suppose that you have been given the table structure and data shown in Table 6.9,
which was imported from an Excel spreadsheet. The data reflect that a professor can
have multiple advisees, can serve on multiple committees, and can edit more than
one journal.
4
INF2603/202
Table 3.1: Sample PROFESSOR Records
Attribute Name
Sample Value
Sample Value
Sample Value
EMP_NUM
PROF_RANK
EMP_NAME
DEPT_CODE
DEPT_NAME
123
Professor
Ghee
CIS
Computer Info.
Systems
KDD-567
1215, 2312, 3233,
2218, 2098
104
Asst. Professor
Rankin
CHEM
Chemistry
118
Assoc. Professor
Ortega
CIS
Computer Info.
Systems
KDD-562
2134, 2789, 3456,
2002, 2046, 2018,
2764
PROF_OFFICE
ADVISEE
COMMITTEE_CODE
JOURNAL_CODE
PROMO, TRAF
APPL, DEV
JMIS, QED,
JMGT
BLF-119
3102, 2782, 3311,
2008, 2876, 2222,
3745, 1783,
2378
DEV
SPR, TRAF
Sample Value
Assoc. Professor
Smith
ENG
English
PRT-345
2873, 2765, 2238,
2901, 2308
PROMO, SPR
DEV
JCIS, JMGT
Given the information in Table 3.1:
a. Draw the dependency diagram.
The dependency diagram is shown in Figure 3.1.
Figure 3.1 The Dependency Diagram for Problem 3.a
EMP_NUM
PROF_RANK
EMP_NAME
DEPT_CODE
DEPT_NAME PROF_OFFICE
transitive dependency
If each professor has a private office, PROF_OFFICE is a determinant of EMP_NUM. However,
if an office can be shared among two or more professors, the dependency shown here does not exist.
Because this dependency is not clear-cut, the dependency line is shown as a dashed line.
ADVISEE
COMMITTEE_CODE
JOURNAL_CODE
Note that Figure 3.1 reflects several ambiguities. For example, although each
PROF_OFFICE value shown in Table 3.1 is unique, does that limited information indicate
5
that each professor has a private office? If so, the office number identifies the professor who
uses that office. This condition yields a dependency. However, this dependency is not a
transitive one, because a non-key attribute, PROF_OFFICE, determines the value of a key
attribute, EMP_NUM. (We have indicated this potential transitive dependency through a
dashed dependency line.)
NOTE
The assumption that PROF_OFFICE → EMP_CODE is a rather restrictive
one, because it would mean that professors cannot share an office. One
could safely assume that administrators at all levels would not care to be
tied by such a restrictive office assignment requirement. Therefore, we will
remove this restriction in the remaining problem solutions.
Also, note that there is no reliable way to identify the effect of multivalued attributes on the
dependencies. For example, EMP_NUM = 123 could identify any one of five advisees.
Therefore, knowing the EMP_NUM does not identify a specific ADVISEE value. The same is
true for the COMMITTEE_CODE and JOURNAL_CODE attributes. Therefore, these
attributes are not marked with a solid arrow line. However, if you know that EMP_NUM =
123, you will also know all five advisees, all four committee codes, and all three journal
codes for that employee number value. But you do not have a unique identification for each
of those attribute values. Therefore, you cannot conclude that EMP_NUM → ADVISEE, nor
can you conclude that EMP_NUM → COMMITTEE_CODE or that EMP_NUM →
JOURNAL_CODE.
b. Identify the multivalued dependencies.
Table 3.1 shows several professor attributes – ADVISEE, COMMITTEE_CODE, and
JOURNAL_CODE -- that represent multivalued dependencies.
c. Create the dependency diagrams to yield a set of table structures in 3NF.
The dependency diagrams are shown in Figure 3.2. Note that we have assumed that it is
possible that professors can share an office.
Figure 3.2 The Dependency Diagram for Problem 3c
6
INF2603/202
EMP_NUM
PROF_RANK
ADVISEE
DEPT_CODE
EMP_NAME
PROF_OFFICE
COMMITTEE_CODE
DEPT_NAME
3NF
JOURNAL_CODE
3NF
7
d. Eliminate the multivalued dependencies by converting the affected table structures
to 4NF.
The structures shown in Figure 3.3 conform to the 4NF requirement. Yet this normalization
does not yield a viable database design. Here is another opportunity to stress that
normalization without data modeling is a poor way to generate useful databases. (Note that
we have assumed that an advisee can have only one advisor, but that an advisor can have
many advisees.)
Figure 3.3 The Initial Dependency Diagrams for Problem 3d
EMP_NUM
PROF_RANK
ADVISEE
EMP_NUM
EMP_NAME
EMP_NUM
COMMITTEE_CODE
EMP_NUM
JOURNAL_CODE
PROF_OFFICE
DEPT_CODE
DEPT_NAME
Problem: This “solution” has limited value, because the
Relationship between EMP_NUM and JOURNAL_CODE
and between EMP_NUM and COMMITTEE_CODE is M:N.
(A professor can write for many journals and each journal
includes articles by many professors. Similarly, a professor
can serve on many committees and each committee is composed of several professors.)
The dependency diagrams shown in Figure 3.3 constitute an attempt to eliminate the
shortcomings of the “system” shown in Figure 3.2. Unfortunately, while this solution meets
the normalization requirements, it lacks the ability to properly link the professors to
committees and journals. (That’s because the relationships between professors and journals
and between professors and committees are M:N.) This solution would yield tables 3.2 and
3.3. (One would expect a professor to be an employee, so it’s reasonable to assume that –
at some point -- we’ll have to create a supertype/subtype relationship between employee
and professor. (To save space, we show only the first three EMP_NUM value sets from
Table 3.1)
8
INF2603/202
Table 3.2 Implementation of the M:N Relationship between
EMP_NUM and COMMITTEE_CODE
EMP_NUM
COMMITTEE_CODE
123
PROMO
123
TRAF
123
APPL
123
JMGT
104
DEV
118
SPR
118
TRAF
The PK of the table shown in Table 3.2 is EMP_NUM + COMMITTEE_CODE.
Table 3.3 Implementation of the M:N Relationship between
EMP_NUM and JOURNAL_CODE
EMP_NUM
JOURNAL_CODE
123
JMIS
123
QED
123
JMGT
118
JCIS
118
JMGT
The PK of the table shown in Table 3.3 is EMP_NUM + JOURNAL_CODE. Because
EMP_CODE = 104 does not show any entries in the JOURNAL_CODE, the employee code
does not occur in Table 3.3.
The preceding table structures create multiple redundancies. Therefore, this solution is not
acceptable. Here is yet another indication that normalization, while very useful, is not always
(usually?) capable of producing implementable solutions. For example, the preceding
examples illustrate that mulivalued attributes and M:N relationships cannot be effectively
modeled without first using the ERD. (After the ERD has done its work, you should, of
course, use dependency diagrams to check for data redundancies!) Figure 3.4 shows a
more practical solution to the problem and its structures all conform to the normalization
requirements.
9
e. Draw the Crow’s Foot ERD to reflect the dependency diagrams you drew in Part c.
(Note: You might have to create additional attributes to define the proper PKs and
FKs. Make sure that all of your attributes conform to the naming conventions.)
Given the discussion in the previous problem segment d, we have incorporated additional
features in the Crow’s Foot ERD shown in Figure 3.4. Note that we have eliminated the M:N
relationships in this design by creating composite entities. This design is implementable and
it meets design standards. Normalization was part of the process that led to this solution, but
it was only a part of that solution. Normalization does not replace design!
Figure 3.4 The Crow’s Foot ERD for Problem 3e
10
INF2603/202
Question 4
[7]
a. What three join types are included in the OUTER JOIN classification?
(3)
Read page 85 and 212-284 about different Outer Join classes (1 mark for each)
b. What is the difference between the COUNT aggregate function and the SUM aggregate
function?
(2)
Read page 282 – 284 (1 mark for explaining each)
c. What Oracle function should you use to calculate the number of days between your birthday
and the current date?
(2)
Read about Oracle DATE FUNCTIONS on Table 7.9, page 304 to 305.
NB: For subtracting your birthdate from the current date, using date arithmetic, the number
of dates will be returned (1 mark for this). Note that in Oracle, the SQL statement requires
the use of the FROM clause (1 mark for using virtual table called DUAL).
Question 5
[19]
Consider the contents of the ASSIGNMENT table and use SQL commands to answer questions
5a–e .
Table 5.1: ASSIGNMENT
11
NOTE: All SQL syntax must be correct, missing characters will be penalized!
a. Write the SQL query to list the assignmnet umber, project number, employee number and
assignment charge per hour for all the projects that were assigned after the 24 th of March
2018.Sort the results by employee number.
(3)
b. Write the SQL code that will list only the distinct project numbers in the ASSIGNMENT table,
sorted by project number.
(4)
c. Write the SQL code to validate the ASSIGN_CHARGE values in the ASSIGNMENT table.
Your quesry shoul retrieve the assignment number, employee number, project number, the
stored assignment charge (ASSIGN_CHARGE), and the calculated assignment charge
(calculated by multiplying ASSIGN_CHG_HR by ASSIGN_HOURS). Sort the results by the
assignment number.
(5)
Wrong question given to students, not refering to the given tables:
d. Write the SQL query to display the book number, title, and cost for all books that cost
R599.95 sorted by book number as in the table below.
(2)
Correct questions: Please use this TABLE:
BOOK (Book_Num, Book_Title, Book_Year, Book_Cost, Book_Subject, Pat_ID)
Write the SQL query to display the book number, title, and cost for all books that cost
R599.95 sorted by book number as in the table below.
(2)
The students received free 2 marks, although most students got it right.
e. Write a query to produce the total number of hours and charges for each of the projects
represented in the ASSIGNMENT table, sorted by project number. The output is shown
below:
PROJ_NUM
12
(5)
SumOfASSIGN_HOURS
SumOfASSIGN_CHARGE
15
20.5
1806.52
18
23.7
1544.80
22
27.0
2593.16
25
19.4
1668.16
INF2603/202
ANSWER
Consider the contents of the ASSIGNMENT table and use SQL commands to answer questions
5a–e .
Table 6.1: ASSIGNMENT
NOTE: All SQL syntax must be correct, missing characters will be penalized!
a. Write the SQL query to list the assignmnet umber, project number, employee number and
assignment charge per hour for all the projects that were assigned after the 24th of March
2018.Sort the results by employee number.
(3)
ANSWER
SELECT AAIGN_NUM, PROJ_NUM, EMP_NUM, ASSIGN_CHG_HR
FROM ASSIGNMENT
WHERE ASSIGN_DATE> “24 MARCH 2018”
ORDER BY EMP_NUM;
13
b. Write the SQL code that will list only the distinct project numbers in the ASSIGNMENT table,
sorted by project number.
(4)
ANSWER
SELECT DISTINCT PROJ_NUM
FROM ASSIGNMENT
ORDER BY PROJ_NUM;
c. Write the SQL code to validate the ASSIGN_CHARGE values in the ASSIGNMENT table.
Your query should retrieve the assignment number, employee number, project number, the
stored assignment charge (ASSIGN_CHARGE), and the calculated assignment charge
(calculated by multiplying ASSIGN_CHG_HR by ASSIGN_HOURS). Sort the results by the
assignment number.
(5)
ANSWER
SELECT
ASSIGN_NUM,
EMP_NUM,
PROJ_NUM,
ASSIGN_CHARGE,
ROUND(ASSIGN_CHG_HR * ASSIGN_HOURS, 2) AS CALC_ASSIGN_CHARGE
FROM ASSIGNMENT
ORDER BY ASSIGN_NUM;
d. Write the SQL query to display the book number, title, and cost for all books that cost
R599.95 sorted by book number as in the table below.
(2)
The question was refering to the table of other assignment, hence we gave you free 2 marks
e. Write a query to produce the total number of hours and charges for each of the projects
represented in the ASSIGNMENT table, sorted by project number. The output is shown
below:
(5)
ANSWER
PROJ_NUM
14
SumOfASSIGN_HOURS
SumOfASSIGN_CHARGE
15
20.5
1806.52
18
23.7
1544.80
22
27.0
2593.16
25
19.4
1668.16
INF2603/202
ANSWER
SELECT PROJ_NUM, ROUND(Sum(ASSIGN_HOURS), 1) AS SumOfASSIGN_HOURS,
ROUND(Sum(ASSIGN_CHARGE), 2) AS SumOfASSIGN_CHARGE
FROM ASSIGNMENT
GROUP BY PROJ_NUM
ORDER BY PROJ_NUM;
©
2019
15