Databases

Question 1

What is a data model?

Answer 1

An abstract model of which things to store and what information about them should be recorded.

Question 2

What is an Entity?

Answer 2

An object, event, person or thing about which data is to be stored

Question 3

What is an attribute?

Answer 3

Attributes are characteristics or other information about entities

Question 4

How are databases formed?

Answer 4

They are formed of tables which are used to store multiple entities

Question 5

What is the notation for an entity description?

Answer 5

Entity1 (Attribute1, Attribute2 ….)
-The primary key is always underlined

Example: Patient (Title, Firstname, Surname, Address, Email)

Question 6

What is an entity identifier?

Answer 6

• An attribute given to each entity which is unique within that table.
• Also known as the primary key.

Question 7

What is a requirement of primary keys (entity identifiers)?

Answer 7

They must be unique

Question 8

What are the three types of relationships entities can have with each other?

Answer 8

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

Question 9

What is an Entity relationship diagram?

Answer 9

They graphically represent the relationships between tables/entities in a database

Question 10

What does it mean when entities have a link between them in an Entity relationship diagram?

Answer 10

That the two entities are related in some way,

Question 11

What 2 things show a relationship in an Entity relationship diagram?

Answer 11

• Both the degree and the name of the relationship need to be specified
• For example: Head teacher ——————– School
  The degree: One-to-one
  The name: In charge of

Question 12

What type of key is formed of multiple attributes, combined to form the primary key?

Answer 12

A composite key

Question 13

What is a composite primary key?

Answer 13

A key formed of multiple attributes, combined to form the primary key
(also known as just a composite key)

Question 14

What is a primary key?

Answer 14

an attribute that uniquely identifies every entity in a database

Question 15

What is a foreign key?

Answer 15

• An attribute that is a primary key in another table

- The attribute exists in both tables

Question 16

How is the primary key and foreign represented in an entity description?

Answer 16

-The primary key has an asterisk next to it
For example: PatientID *
-The foreign key is in italics

Question 17

When is a link table used?

Answer 17

• It’s used to represent many-to-many relationships

- It creates a third table (the linking table) as many to many relationships are impossible to represent on a computer

Question 18

What is a relational database?

Answer 18

A database that is formed of multiple tables that are linked together by common attributes

Question 19

How is a record with a primary key quickly located?

Answer 19

An index of the primary key and is automatically maintained by the database software, it gives the position of every record according to its primary key

Question 20

What is Normalisation?

Answer 20

The process used to make the design of a database the most efficient without compromising the integrity of the data

Question 21

What are the advantages of normalising a database

Answer 21

• It allows for faster searching and sorting and saves storage space as it creates smaller tables
• They are easier to maintain.
• Data consistency is improved, reducing the number of anomalies that occur.
• Data integrity is maintained as there is no unnecessary duplication of data.

Question 22

When is a database in first normal form?

Answer 22

If the database contains no repeating attribute/group of attributes

Question 23

What does atomic mean?

Answer 23

It means that no single column contains more than one value

Question 24

When is a database in second normal form?

Answer 24

• It must satisfy first normal form

- Contains no partial key dependencies

Question 25

What is a partial key dependency?

Answer 25

When attributes depend on only one part of the primary key (only happens when the primary key is a composite primary key)

Question 26

When is a database in third normal form?

Answer 26

- It must satisfy second normal form | - It must have no non-key dependencies

Question 27

What is a non-key dependency?

Answer 27

Where the value of an attribute is determined by the value of another attribute which is not part of the key

Question 28

What does a client server database system provide?

Answer 28

It provides simultaneous access to a database for multiple clients

Question 29

What is concurrent access?

Answer 29

It's a problem caused when multiple users attempt to access/update the same field in database at the same time

Question 30

What problems can concurrent access lead to?

Answer 30

It can result in updates being lost if two users edit a record at the same time

Question 31

What are the 4 methods for dealing with concurrent access?

Answer 31

- Record locks - Serialisation - Timestamping - Commitment ordering

Question 32

How does record locks solve the problem of concurrent access?

Answer 32

- When a user accesses a record, it is immediately locked to other users until the first user has finished using it. Other users can't access the content of a field until it has been unlocked

Question 33

How does Serialisation solve the problem of concurrent access?

Answer 33

- Requests from other users are placed in a queue. | - Once the first user has finished, the next command in the queue is executed

Question 34

How does Timestamp ordering solve the problem of concurrent access?

Answer 34

- When multiple commands are sent to the same field in a database, each is assigned a timestamp which marks the point in time at which the command was initiated. - Commands are carried out on the field in the order of their timestamps.

Question 35

How does Commitment ordering solve the problem of concurrent access?

Answer 35

- Uses an algorithm work out the optimum order in which to execute commands for a field. - The algorithm takes into account the impact of commands on the rest of the database - It attempts to minimise issues occuring.

Question 36

What are the characteristics of serial files?

Answer 36

- Data is stored in the order in which it was entered - No order to the data is maintained - useful for storing transactional data or initialisation files

Question 37

What are the characteristics of serial files?

Answer 37

- Store data in order of a key field - The order is maintained when new records are added - useful for storing master files

Question 38

What is a flat file database?

Answer 38

A database composed of one table/file

Question 39

What is a database?

Answer 39

Structured, persistent collections of data

Question 40

What are the advantages of using databases?

Answer 40

- Makes processing more efficient - Avoids redundancy - Allows users to only see relevant data - Saves Storage space

Question 41

What do database management systems (DBSM) provide?

Answer 41

- Additional security, provides a centralised automatic backup - Program/data independence - Integrity to ensure efficiency and structure is not compromised - A manipulation language to access/change the data

Question 42

What does program/data independence mean?

Answer 42

- Data is separated from programs that can access it | - Advantage being that software tools that control the database can be modified without affecting the data