8.1 Databases.concepts

Question 1

What is a database?

Answer 1

A structured collection of data items that can be accessed by different application programs.

Question 2

What is a relational database?

Answer 2

A database where data items are linked by internal pointers.

Question 3

What is a table in a database?

Answer 3

A group of similar data with rows for each instance of an entity and columns for each attribute.

Question 4

What is a record in a database?

Answer 4

A row in a table representing one instance of an entity.

Question 5

What is a field in a database?

Answer 5

A column in a table representing an attribute of the entity.

Question 6

What is a tuple in a database?

Answer 6

One instance of an entity, represented by a row in a table.

Question 7

What is an entity in a database?

Answer 7

Anything that can have data stored about it, such as a person, place, event, or thing.

Question 8

What is an attribute in a database?

Answer 8

An individual data item stored for an entity, like a name, address, or date of birth.

Question 9

What is a candidate key?

Answer 9

An attribute or smallest set of attributes where no two tuples have the same value.

Question 10

What is a primary key?

Answer 10

A unique identifier for a table, which is a special case of a candidate key.

Question 11

What is a secondary key?

Answer 11

A candidate key that serves as an alternative to the primary key.

Question 12

What is a foreign key?

Answer 12

A set of attributes in one table that refers to the primary key in another table.

Question 13

What is a relationship in a database?

Answer 13

A situation where a table has a foreign key that refers to a primary key in another table.

Question 14

What is referential integrity?

Answer 14

A database property ensuring no foreign key values exist without matching the corresponding primary key.

Question 15

What is an index in a database?

Answer 15

A data structure built from one or more columns in a table to speed up searching.

Question 16

What is an Entity-Relationship (E-R) model or diagram?

Answer 16

A graphical representation of a database and the relationships between entities.

Question 17

What is normalisation in a database?

Answer 17

The process of organising data into two or more tables and relationships to minimise redundancy.

Question 18

What is First Normal Form (1NF)?

Answer 18

A relational database status where entities do not contain repeated groups of attributes.

Question 19

What is Second Normal Form (2NF)?

Answer 19

A database in 1NF where non-key attributes depend entirely on the primary key.

Question 20

What is Third Normal Form (3NF)?

Answer 20

A database in 2NF where all non-key attributes are independent of each other.

Question 21

What is a composite key?

Answer 21

A set of attributes that together form the primary key to uniquely identify a table record.

Question 22

What is a file in computing?

Answer 22

A collection of items of data, often structured as records made up of fields containing data about the same ‘thing’.

Question 23

What is a data item?

Answer 23

An individual element of data within a record or field.

Question 24

How does the organisation of records in a program affect data processing?

Answer 24

Records can be fixed or variable in length and may contain information about their structure, requiring programs using them to follow the same structure.

Question 25

Why can record structure cause issues in file-based systems?

Answer 25

If one program changes the structure, all other programs using the file must be updated; failure to do so can cause data handling errors.

Question 26

What is one limitation of a file-based approach?

Answer 26

Storage space is wasted due to data duplication and redundancy.

Question 27

How can data inconsistency arise in a file-based approach?

Answer 27

If one application alters data and another does not, the data becomes inconsistent.

Question 28

Why is data independence limited in a file-based approach?

Answer 28

Enquiries depend on the data structure and software used, making the data not truly independent.

Question 29

How does the BCS Glossary of Computing define a database?

Answer 29

A large collection of data items and links between them, structured for access by different applications programs.

Question 30

How does CJ Date define a database?

Answer 30

An electronic filing cabinet allowing tasks like adding, inserting, retrieving, updating, and cross-referencing data.

Question 31

What is a simple definition of a database?

Answer 31

A structured collection of data items that can be accessed by different applications programs.

Question 32

How is data typically structured in a database?

Answer 32

As a collection of records, where each record contains fields with data about the same 'thing'.

Question 33

What is a relational database?

Answer 33

A database where data items are linked by internal pointers.

Question 34

List one benefit of the database approach regarding storage.

Answer 34

Data items are stored only once, reducing redundancy and saving storage space.

Question 35

How does the database approach ensure data consistency?

Answer 35

Data altered in one application is automatically available in other applications.

Question 36

Why is data independence a benefit of the database approach?

Answer 36

Enquiries do not depend on the data structure or software used, allowing flexibility in data access.

Question 37

What is a table in a relational database?

Answer 37

A group of similar data with rows for each entity instance (tuples) and columns for each attribute (fields).

Question 38

What is a record (or tuple) in a relational database?

Answer 38

A row in a table representing one instance of an entity.

Question 39

What is a field (or attribute) in a relational database?

Answer 39

A column in a table representing a single data item stored for an entity.

Question 40

Define 'entity' in the context of a relational database.

Answer 40

Anything that can have data stored about it, such as a person, place, event, or object.

Question 41

How is data consistency maintained in a relational database?

Answer 41

By controlling or automating updates and minimising duplicate data copies through pointers (keys).

Question 42

What is a candidate key?

Answer 42

An attribute or the smallest set of attributes that uniquely identify a tuple in a table.

Question 43

What is a primary key?

Answer 43

A unique identifier for a table; it is a special case of a candidate key.

Question 44

What is a secondary key?

Answer 44

A candidate key that serves as an alternative to the primary key.

Question 45

What is a foreign key?

Answer 45

An attribute in one table that refers to the primary key in another table, creating a relationship.

Question 46

How is a relationship formed in a relational database?

Answer 46

When a table contains a foreign key that refers to a primary key in another table.

Question 47

What is referential integrity?

Answer 47

Ensuring that every foreign key value in a table matches a primary key value in the referenced table.

Question 48

What are the types of relationships in a relational database?

Answer 48

One-to-one (1:1), one-to-many (1:m), many-to-one (m:1), and many-to-many (m:m).

Question 49

What is the purpose of an index in a relational database?

Answer 49

To speed up searching for data by creating a data structure from one or more columns in a table.

Question 50

What is the purpose of an Entity-Relationship (E-R) diagram?

Answer 50

To provide a visual representation of how entities in a database are related.

Question 51

What does the term 'cardinality' mean in an E-R diagram?

Answer 51

It defines the type of relationship and whether it is mandatory or optional between entities.

Question 52

Give an example of an optional relationship in an E-R diagram.

Answer 52

The relationship between desk and employee is optional (zero or one) since some desks might be unassigned.

Question 53

Give an example of a mandatory relationship in an E-R diagram.

Answer 53

The relationship between mother and child is mandatory (one or many) because every mother must have at least one child.

Question 54

What is the purpose of normalisation in database design?

Answer 54

To reduce data redundancy and ensure data integrity in a relational database.

Question 55

What happens if a database is not normalised?

Answer 55

It will be larger, harder to update, and more difficult to extract data for queries.

Question 56

What is First Normal Form (1NF)?

Answer 56

A state where entities do not contain repeated groups of attributes.

Question 57

What is Second Normal Form (2NF)?

Answer 57

A state where entities are in 1NF and every non-key attribute depends on the whole primary key with no partial dependencies.

Question 58

What is Third Normal Form (3NF)?

Answer 58

A state where entities are in 2NF, and all non-key attributes are independent of each other and only depend on the primary key.

Question 59

What is the key rule for a database in 3NF?

Answer 59

All attributes in a table depend upon the key, the whole key, and nothing but the key.