Database Fundamentals 3

Question 1

Attribute

Answer 1

Named column in relational table.

It draws values from the domain

Question 2

Domain

Answer 2

The set of possible values for the attribute

Question 3

Degree

Answer 3

Number of attributes

Question 4

Cardinality

Answer 4

Number of rows

Question 5

Key

Answer 5

A key is one or more attributes that determine other attributes.

Question 6

Composite key

Answer 6

Composed of more than one attribute

Question 7

Types of relational database keys

Answer 7

1. Superkey
2. Candidate key
3. Primary key
4. Secondary key
5. Foreign key

Question 8

Superkey

Answer 8

An attribute (or combination of attributes) that uniquely identifies each row in a table.

Question 9

Candidate key

Answer 9

A minimal (irreducible) superkey. A superkey that does not contain a subset of attributes that is itself a superkey.

Question 10

Primary key

Answer 10

A candidate key selected to uniquely identify all other attribute values in any given row. Cannot contain null values.

Question 11

Secondary key

Answer 11

An attribute (or combination of attributes) used strictly for data retrieval purposes.

Question 12

Foreign key

Answer 12

An attribute (or combination of attributes) in one table whose values must either match the primary key in another table or be null.

Question 13

What can Nulls represent?

Answer 13

1. An unknown attribute value.
2. A known, but missing, attribute value.
3. A “not applicable” condition.

Question 14

What do flags do?

Answer 14

Flags indicate the absence of some value

Question 15

What is controlled redundancy?

Answer 15

Control data redundancy by using common attributes shared by tables.

Foreign keys make the relational database work, and enables tables to be linked together. This is crucial to exercising data redundancy control.

Question 16

What are Integrity Rules?

Answer 16

1. Entity Integrity:
   - Requirement: All primary key entries are unique, and no part of a primary key may be null.
   - Purpose: Each row will have a unique identity, and foreign key values can properly reference primary key values.
2. Referential Integrity:
   - Requirement: A foreign key may have either a null entry, as long as it is not a part of the table’s primary key, or an entry that matches the primary key value in a table to which it is related.
   - Purpose: It is possible for an attribute NOT to have a corresponding value, but it will be impossible to have an invalid entry. The enforcement of the referential integrity rule makes it impossible to delete a row in one table whose primary key has mandatory matching foreign key values in another table.

Question 17

What is The Data Dictionary?

Answer 17

It provides detailed accounting of all tables found within the database.

It contains (at least) all the attribute names and characteristics for each table in the system.

It also contains metadata, also known as the metadata repository.

Question 18

1:M Relationship

Answer 18

Should be the norm in any relational database design

Question 19

1:1 Relationship

Answer 19

Should be rare in any relational database design.

One entity relates to only one other entity and vice versa.

Sometimes this means that entity components were not defined properly.

This could indicate that two entities actually belong in the same table.

Question 20

M:N Relationships

Answer 20

Cannot be implemented as such in the relational model.

You can avoid problems inherent to M:N relationships by creating a composite/bridge entity. It is implemented by breaking it up into a set of 1:M relationships. It includes as foreign keys the primary keys of tables to be linked.

Question 21

What are indexes?

Answer 21

Orderly arrangement to logically access rows in a table.

Each index is associated with only ONE table.

Main purpose: To optimize query speed.

Question 22

Index key

Answer 22

Index’s reference point.

Points to data location identified by the key.

Question 23

Unique index

Answer 23

Index in which the index key can have only one pointer value (row) associated with it.