CGS2541 Project 4 Answer Form
Name
Marilynn A. Diller
Section #
2541/25287
1. What is an entity supertype, and why is it used?
An entity supertype is a non specific entity that embodies standard features of entity subtypes.
The entity supertype is related to the subtypes. An entity supertype is used to reduce nulls and
redundancy in relationships.
2. What kinds of data would you store in an entity subtype?
The data stored in an entity subtype is specific, unique characteristics of their own that are
inherited through all attributes/relationships of the entity supertype.
3. What primary key characteristics are considered desirable? Explain why each
characteristic is considered desirable.
A primary key must assure that each entity inset and row within the table is uniquely identified
through a value. The primary key certifies entity integrity and cannot contain nulls. A primary
key sets the value of dependent attributes, implementing the least amount of attributes which
characterize an entity instance.A primary key will not change over time, will be nonintelligent,
single-attribute, numeric driven, and be security compliant.
4. Under what circumstances are composite primary keys appropriate?
Composite primary keys are appropriate to use when each primary key combination is only
used once in a M:N relationship and they are the identifiers of composite entities. Composite
primary keys can be identifiers for weak entities when a strong identifying relationship lies
with a parent entity.
5. What is a specialization hierarchy?
A specialization hierarchy is a top down process of identifying entity supertypes or parent
entities with entity subtypes or child entities. It is arranged by a higher level supertype grouping
unique characteristics that are directly related with lower level entity subtypes. A subtype can
only exist inside a supertype context. Many levels of supertype and subtype relationships can
exist in a specialization hierarchy due to the many subtypes a supertype can be directly related
with.
For questions 6 – 8, refer to the Figure below:
CGS2541 Project 4 Answer Form
6. List all of the attributes of a movie.
Prod_Num, Prod_Title, Prod_Release Date, Prod_Price, Prod_Type, Movie_Rating and
Movie_Director
7. According to the data model, is it required that every entity instance in the PRODUCT
table be associated with an entity instance in the CD table? Why or why not?
It is not required since the disjoin total completeness constraint is based on the Product number
involved with all three subtypes limiting subtypes to only be required to unique value instance.
8. Is it possible for a book to appear in the BOOK table without appearing in the
PRODUCT table? Why or why not?
It is not possible due to subtypes only existing within the context of the supertype.
9. The design of the CGS2541 Project 4 Ch05_TinyCollege.accdb database attached in the
instructions reflects business rules such as “a professor may advise many students” and
“a professor may chair one department.” Modify the current ERD relationship diagram
to include these business rules:
 An employee could be staff or a professor or an administrator.
 A professor may also be an administrator.
 Staff employees have a work level classification, such a Level I and Level II.
 Only professors can chair a department. A department is chaired by only one professor.
 Only professors can serve as the dean of a college. Each of the university’s colleges is
served by one dean.
CGS2541 Project 4 Answer Form


A professor can teach many classes.
Administrators have a position title.
Given that information, create the complete ERD containing all primary keys, foreign keys,
and main attributes. (Hint use Subtypes for Employees)
10. Tiny College wants to keep track of the history of all administrative appointments (date
of appointment and date of termination). (Hint: Time variant data are at work.) The Tiny
College chancellor may want to know how many deans worked in the College of Business
between January 1, 1960 and January 1, 2010 or who the dean of the College of Education
was in 1990. Given that information, create the complete ERD containing all primary
keys, foreign keys, and main attributes.
CGS2541 Project 4 Answer Form