Chapter 16 - Database concepts

Question 1

What is an entity?

Answer 1

» Entity is a category of object,person,event or thing of interest to an organisation about which data is to be recorded

Question 2

What does each entity in a database have?

Answer 2

» List of attributes/fields

Question 3

What is another name for a simple database?

Answer 3

» Called a flat file, consiting of information about a single entity - consisting of a single file

Question 4

What is the format of an entity discription?

Answer 4

» Entity1(Attribute1, Attribute2…)

Question 5

What is an example of a discription for an entity which is called product?

Answer 5

» Product(Title,Subject,Author,Length)

Question 6

What is needed to uniquely identify the entity?

Answer 6

» An Identifier

Question 7

What is the identifier known as in a relational database?

Answer 7

» Primary key

Question 8

What is the purpose of the primary key?

Answer 8

» To identify a particular record relationship database

Question 9

What is the format for a primary key?

Answer 9

» Customer(CustId,title,firstname)
» CustId is the primary key in this instant as it is unique

Question 10

Why is a secondary index needed

Answer 10

» To search the database quickly such as the surname in a patients file

Question 11

What is a composite primary key?

Answer 11

» A primary key which consists of more than one attribute is called a composite primary key

Question 12

What are the 3 different degrees of relationship between 2 entities?

Answer 12

» One-to-one
» One-to-many
» Many-to-many

Question 13

What is an example of a one to one relationship?

Answer 13

» A husband and wife

Question 14

What is an example of a one to many relationship?

Answer 14

» Mother and a child
» As a mother may have many children, but each child has the same mother

Question 15

What is an example of a many to many relationship?

Answer 15

» Film and actor

Question 16

What is the purpose of an entity relationship diagram?

Answer 16

» A diagrammatic way of representing the relationships between the entities in a databse

Question 17

What 2 things needed to be specified in a E-R diagram?

Answer 17

» The degree of relationship
» The name of the relationship

Question 18

Describe the E-R diagram of a Headteacher and a School

Answer 18

» One to one relationship
» Headteacher in charge of School

Question 19

What is created in a relational database?

Answer 19

» A seperate table is created for each entity identified in thre system

Question 20

What is the foreign key?

Answer 20

» An extra field/attribute that links the 2 tables

Question 21

What is the purpose of the Foreign key?

Answer 21

» An attribute that creates a join between two tables
» Attribute that is common to both tables
» Primary key in one table is the foreign key in the table to which it is linked

Question 22

What is the primary key indicated by?

Answer 22

» Asterisk

Question 23

What is the foreign key indicated by?

Answer 23

» Italics

Question 24

How is the one-to-one degree shown in an E-R diagram?

Answer 24

» A straight line

Question 25

How is the one-to-many relation shown in an E-R diagram?

Answer 25

» A straight line from the entity which is the one relationship to a crows foot in the entity which is the many

Question 26

How is the Many to Many relationship shown on an E-R diagram?

Answer 26

» 2 crows foots linking the entities

Question 27

What are tables also reffered by?

Answer 27

» Relations

Question 28

What is the structure of a relational database?

Answer 28

» Excel spreadsheet
» Each row containing entities
» Column containing attributes belonging to the records

Question 29

What is a record?

Answer 29

» A row in a database

Question 30

What is the problem of linking tables in a many-to many relaionship?

Answer 30

» Tables cannot be directly linked

Question 31

How can you resolve the issued of tables not being linked in a many-many relation in an E-R diagram?

Answer 31

» An extra table is needed to linke the 2 tables

Question 32

What is the important thing to remember when an entity is used in the a table?

Answer 32

» It is not delted in the table

Question 33

What is Referential integrity?

Answer 33

» It is the logical dependency of a foreign key on a primary key
» Means the reference from a row in one table to another table must be valid
» Values in that key match the values in a key in a related table