Chapter 5 Flashcards
What is Specialization Hierarchy?
Depicts arrangement of higher-level entity supertypes (parent) and lower-level entity subtypes (child).
Relationships are described in terms of “is-a(n)” relationships
What is Supertype and Subtypes?
Supertype = Parent entity
Subtypes = Child entity
Supertype for example employee
Subtypes for example Pilot, Mechanic, Accountant
What is Data Normalization?
An improvement you do. For example minimize redundancy. DB Normalization can have three forms: 1NF, 2NF, 3NF.
What is the purpose of conversion to 1NF? And what are the steps?
Enable reducing data redundancies.
Steps:
-Eliminate the repeating groups.
-Identify the primary key.
-Identify all dependencies.
What is Partial Dependency?
A,B –> C,D
For example, when the teacher is putting the marks, he/she has to match the ID-number or student name and then enter the mark. She/he does not need both student number and student name.
What is Transitive Dependency?
A depends on B, B depends on C. Then A is transitive dependency of C.
What are the steps when conversion to 2NF? And what is 2NF connected to?
-Make new tables to eliminate partial dependencies.
-Reassign corresponding dependent attributes.
2NF is connected to the Partial Dependency.
What is an Entity supertype?
Generic entity type related to one or more entity subtypes (contains common characters)
What is an Entity subtype?
Contains unique characteristics of each entity subtype
What does Inheritance enable?
Enables an entity subtype to inherit attributes and relationships of the supertype.
All entity subtypes inherit their primary key attribute from their supertype
At the implementation level, supertype and its subtype(s) maintain a 1:1relationship
Entity subtypes inherit all relationships in which supertype entity participates
Lower-level subtypes inherit all attributes from its upper-level supertype
What are Disjoint subtypes (non overlapping subtypes)?
Contain a unique subset of the supertype entity set, example “Employee can’t be Pilot and mechanic at the same time”
What are Overlapping subtypes?
Contain non unique subsets of the supertype entity set
Professor: Y
Administrator: N
The employee is a member of the professor Subtype.
Professor: N
Administrator: Y
The employee is member of the Administrator subtype.
Professor: Y
Administrator: Y
The employee is both a member of the professor and administrator subtype.
What does Completeness Constraint specify?
Specifies whether each supertype occurrence must also be a member of at least one subtype
Types:
Partial completeness: Not every supertype occurrence is a member of a subtype
Total completeness: Every supertype occurrence must be a member of any subtype
