Exam 1-Chapter 3

Question 1

Relational Model

Answer 1

View data logically rather than physically

Question 2

Table

Answer 2

• Two-dimensional structure composed of rows and columns
• Structural an data independence
• Resembles a file conceptually

Question 3

Entity Set

Answer 3

Contains group of related entity occurrences

Question 4

Key

Answer 4

• One or more attributes that determine other attributes
• A key’s role is based on determination (if you know the value of attribute A, you can look up or determine the value of attribute B)

Question 5

Functional Dependence

Answer 5

Attribute B is functionally dependent on the attribute A if each value in column A determines one and only one value in column B

Question 6

Composite Key

Answer 6

Composed of more than one attribute (Combination of LNAME, FNAME, INIT, and PHONE are likely to be unique)

Question 7

Ful Functional Dependence

Answer 7

Attribute B is functionally dependent on a composite key A, but not on any subset of A

Question 8

Key Attribute

Answer 8

Any attribute that is part of a key

Question 9

Superkey

Answer 9

Any key that uniquely identifies each row. A superkey functionally determines all of the entity’s attributers (STU_NUM)

Question 10

Candidate Key

Answer 10

A superkey without unnecessary attributes (a minimal superkey; STU_NUM, STU_LNAME is a superkey but not a candidate key, STU_NUM ins a candidate key)

Question 11

Nulls

Answer 11

No data entry; not permitted in primary key; should be avoided in other attributes; can represent different meaning, such as an unknown attribute value, a known but missing attribute value, and a “not applicable” condition

Question 12

Flags

Answer 12

Designers use flags to avoid nulls. Flags indicate absence of some value

Question 13

Controlled Redundancy

Answer 13

Makes the relational database work. Tables within the database share common attribues

Question 14

Rational Schema

Answer 14

A textual representation of the database tables

Question 15

Foreign Key

Answer 15

An attribute whose values match primary key values in the related table

Question 16

Referential Integrity

Answer 16

Foreign key contains a value that refers to an existing valid tuple (row) in another relation

Question 17

Secondary Key

Answer 17

Key used strictly for data retrieval purposes

Question 18

Entity Integrity Rules Requirement

Answer 18

All primary key entries are unique, and no part of a primary key may be null

Question 19

Reference Integrity Rules Requirement

Answer 19

A foreign key may have either a null entry, as long as it is not a part of its table’s primary key, or an entry that matches the primary key value in a table to which it is related (every non-null foreign key value must reference an existing primary key value

Question 20

Relational Algebra

Answer 20

Defines theoretical way of manipulating table contents using relational operators. Use of relational algebra operators on existing relations produces new relations

Question 21

SELECT

Answer 21

SELECT all rows in a table that satisfy a given condition. Results in a horizontal subset of the table

Question 22

PROJECT

Answer 22

Yields all values for selected attributes. Results in a vertical subset of the table

Question 23

UNION

Answer 23

Combines all rows from two tables, excluding duplicate rows. The tables must be union-compatible (have the same degree (# of columns); columns must be of the same type; column domains (range of permissible values) must be compatible)

Question 24

INTERSECT

Answer 24

Yields only the rows that appear in both tables. The tables must be union-compatible.

Question 25

DIFFERENCE

Answer 25

Yields all rows in one table that are not found in the other table. Subtracts one table from the other. The tables must be union-compatible

Question 26

PRODUCT

Answer 26

Yields all possible rows from two tables. Also known as the Cartesian product

Question 27

JOIN

Answer 27

JOIN combines data from two or more tables. It is the real power behind the relational database. Tables are linked by a common attribute

Question 28

Natural Join

Answer 28

Links tables by selecting rows with common values in common attributes
A three stage process: 1) PRODUCT 2) SELECT 3) PROJECT

Question 29

Inner Join

Answer 29

A join that returns matched records from the tables being joined

Question 30

Outer Join

Answer 30

Inner join+ returns all the matched records from the tables being joined, plus it returns the unmatched records from one of the two tables

Question 31

Left Outer Join

Answer 31

Yields all rows from CUSTOMER table, including those that do not have matching value in the AGENT table

Question 32

Right Outer Join

Answer 32

Yields all rows from AGENT table, including those that do not have a matching value in the CUSTOMER table

Question 33

Data Dictionary

Answer 33

Provides detailed accounting of all tables found within the database; contains (at least) all the attribute names and characteristics for each table in the system; contains metadata

Question 34

System Catalog

Answer 34

Contains metadata; detailed system data dictionary that describes all objects within the database (data dictionary + other information, such as user authorizations and access privileges)

Question 35

1:M Relationship

Answer 35

Relational modeling ideal; should be the norm in any relational database design

Question 36

1:1 Relationship

Answer 36

Should be rare in any relational database design; one entity related to only one other entity, and vice versa

Question 37

M:N Relationship

Answer 37

Cannot be implemented as such in the relational model; an M:N relationship can be changed into two 1:M relationship

Question 38

Data Redundancy

Answer 38

Leads to data anomalies (sometimes, data redundancy is necessary

Question 39

Index

Answer 39

Orderly arrangement used to logically (an quickly) access rows in a table

Question 40

Index Key

Answer 40

Index’s reference point; points to data location identified by the key

Question 41

Unique Index

Answer 41

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

Question 42

Composite Index

Answer 42

An index key can have multiple attributes