Relations

Question 1

Relations - logical construct also known as a table

Answer 1

two dimensional has two pools as rows attributes as columns with a distinct name

Question 2

E F Codd

Answer 2

Relational models creator. use the two terms of synonyms for relation whose contents can be permanently saved for future use

Question 3

Relational database model

Answer 3

Enables logical presentation of the data and its relationships.enables you to view data logically rather than physically. easier to understand than the hierarchical and network models

Question 4

The logical view

Answer 4

Simplicity yields simple. to effective database design methodologies. 3 facilitated by the creation of data relations which are based on logical construct called a relation AKA as a data set in Microsoft Access

Question 5

8 characteristics of a relational table

Answer 5

1 the table is two dimensional structure with rows and columns
2 each row is a tuple and represents a single entity occurrence within the entity set
3 each table column represents an attribute and has a distinct name
4 each intersection of a row and column represents a single data value
5 all values in a column must conform to the same data format. Numeric, character, date, logical
6 each column has a specific range of values known as the attribute domain
7 the order of the Rose and columns does not matter in dbms
8 each table must have a primary key which is an attribute or combination of attributes which uniquely identifies each row

Question 6

Rule of a key

Answer 6

Based on the concept of determination the state in which knowing the value of one attribute makes it possible to determine the value of another

Question 7

Functional dependence

Answer 7

The value of one or more attributes determine the value of one or more of the attributes

Question 8

Determinant or key

Answer 8

The attribute whose value determines another

Question 9

Dependent

Answer 9

The attribute whose value is determined by the other attribute

Question 10

Full functional dependence

Answer 10

The entire collection of attributes in the determinant is necessary for the relationship

Question 11

Key consists of

Answer 11

1 one or more attributes that determine other attributes
2 used to ensure that each row in a table is uniquely identifiable
3 establish relationships among tables
4 insured integrity of the data

Question 12

Types of keys

Answer 12

The composite key
Composed of more than one attribute
Is a part of the key

Question 13

Relational database keys - super key and candidate key

Answer 13

Super key a key that can uniquely identify any role in the table

Candidate key minimal or irreducible super key without any unnecessary attributes does not contain a subset of attributes that is itself a super key and it’s based on a functional full functional dependency can have more than one candidate keys in a table or candidates because they are eligible options from which the designer will choose when selecting the primary key

Question 14

Relational database keys - primary key, foreign key

Answer 14

Primary key is a candidate key selected to uniquely identify all the attributes in a given row in the table cannot contain no entries and controls redundancy that allows the relational model to work

Foreign key is the primary key of one table placed in another table to create a common attribute and is used to ensure referential integrity it’s an attribute or combination of attributes in one table must be a null or a valid value in the primary key of the related table and it can contain duplicates

Question 15

Relational database key- secondary key

Answer 15

Secondary key is used strictly for data retrieval purposes it does not necessarily yield a unique outcome it’s effective in narrowing down a search depending on how restrictive the key is

Question 16

Entity integrity

Answer 16

Row (entity instance) has a primary key. attribute in primary key cannot container null

Question 17

Null

Answer 17

Never allowed in any part of the primary key
Creates problems with functions such as COUNT, AVERAGE and SUM
Special codes are used known as Flags to indicate the absence of some value

Question 18

Referential integrity

Answer 18

Reference of an entity instance by another entity instance is valid
Foreign keys are used
Null entry as long as it’s not a part of the tables primary key
All none null foreign key value must reference and exist in primary key value

Question 19

NULLS

Answer 19

1 Indicate my Flags or special codes - none value
2 NOT NULL placed on a column tincture everyone in the table has a value
3 UNIQUE constraint placed on a column to restrict duplicate values

Question 20

Minimal relational dbms must have

Answer 20

SELECT, PROJECT & JOIN

Question 21

Relational Set Operators

Answer 21

Select 
Project
Union
Intersect
Difference
Join
Divide
Product

Question 22

Joins

Answer 22

Natural
Equijoin
Theta
Inner
Outer

Question 23

Data Dictionay

Answer 23

1 Describes all tables in DB created by user and designer

2 described as the DB designer’s database

Question 24

Relvar AKA structure

Answer 24

The data in the structure would be a relation which is a variable

Question 25

Homonyms

Answer 25

The same name is used to label different attributes

Question 26

Synonyms

Answer 26

Different names to describe the same attribute

Question 27

One to many (1:M)

Answer 27

Norm for relational databases

Question 28

One to one (1:1)

Answer 28

One entity can be related to only one other entity and vice versa

Question 29

Many-to-many (M:N)

Answer 29

1 Implemented by creating a new entity in 1:M relationships with the other entities 2 composite entity (i.e., bridge or associative entity): helps avoid problems inherent to M:N relationships - includes the primary keys of tables to be linked