Tables and Keys

Question 1

What is the significance of the relational model in the context of database systems?

Answer 1

The relational model is the de facto standard implemented in major database systems, providing a standardized approach for storing and querying data. It defines the format for data storage and operations for querying data.

Question 2

What are the key components defined by the relational model?

Answer 2

The relational model defines the format for storing data and the operations for querying that data. It includes the structure of tables, relationships between tables, and operations such as SELECT, INSERT, UPDATE, and DELETE.

Question 3

How is a database described when it conforms to the relational model?

Answer 3

A database conforming to the relational model is referred to as a relational database. It adheres to the principles and guidelines set by the relational model for organizing and managing data.

Question 4

In the relational model, what does the term “format by which data should be stored” refer to?

Answer 4

The “format by which data should be stored” in the relational model refers to the structure of tables, including the definition of columns, data types, and relationships between tables, ensuring a standardized way of organizing data.

Question 5

What operations are specified by the relational model for querying data?

Answer 5

The relational model specifies operations such as SELECT (for querying data), INSERT (for adding new data), UPDATE (for modifying existing data), and DELETE (for removing data), forming the basis for database manipulation.

Question 6

Why is the relational model considered a standard in database systems?

Answer 6

The relational model is considered a standard in database systems because it provides a clear and consistent framework for data organization and manipulation. Its principles are widely implemented across major database systems, promoting interoperability and ease of use.

Question 7

How does adherence to the relational model contribute to database consistency and integrity?

Answer 7

Adherence to the relational model contributes to database consistency and integrity by enforcing standardized rules for data organization and manipulation. This ensures that data relationships are maintained, and operations are performed in a predictable and reliable manner.

Question 8

How does the relational model promote interoperability among different database systems?

Answer 8

The relational model promotes interoperability by establishing a common set of principles and standards, allowing applications and queries developed for one relational database system to work with others that conform to the same model.

Question 9

What advantages does the relational model bring to data management in comparison to other models?

Answer 9

The relational model provides advantages such as simplicity, flexibility, and ease of understanding. It offers a clear structure for data organization, supports complex relationships, and facilitates powerful querying capabilities, making it widely adopted in diverse application domains.

Question 10

What is the significance of domains in a relational schema?

Answer 10

Domains in a relational schema define the types of attributes, similar to types in a programming language. They specify the range of values an attribute can take.

Question 11

Define a relation in the context of a relational schema.

Answer 11

In a relational schema, a relation is a set of tuples. This means it consists of rows, and each row contains a unique combination of attribute values.

Question 12

What is the uniqueness constraint associated with tuples in a relation?

Answer 12

Tuples in a relation must be unique, meaning there can be no duplicate tuples. However, some commercial Database Management Systems (DBMSs) may allow duplicate rows in practice.

Question 13

Why does the order of tuples not matter in a relation?

Answer 13

The order of tuples in a relation doesn’t matter because, in a mathematical set, the elements (tuples) are considered unordered. This characteristic is essential for maintaining consistency and simplicity in relational databases.

Question 14

Is the order of attributes significant in a relation within a relational schema?

Answer 14

No, the order of attributes in a relation does not matter. The structure of a relation is defined by its attributes, and their order does not impact the integrity or functionality of the relational schema.

Question 15

What is a Key in the context of a relational database?

Answer 15

A key is a set of attributes for which no two rows in a table can have the same values. It uniquely identifies each row in the table.

Question 16

Define Superkey and provide an example.

Answer 16

A Superkey is a set of one or more attributes whose combined values are unique, meaning no two tuples can have the same values on these attributes. Example: In the PROF table, {pid}, {pid, name}, {pid, dept}, {pid, rank, sal} are all superkeys.

Question 17

What is a Candidate Key, and why is it important?

Answer 17

A Candidate Key in a table is a minimal set of attributes for which no two tuples can have the same values. It is essential because it uniquely identifies each tuple and is designated when the table is created. Every table should have at least one candidate key.

Question 18

Can there be multiple Superkeys for a given table?

Answer 18

Yes, there can be multiple superkeys for a given table. A superkey is “super” because it is a superset of some key and, therefore, there may be more than one way to uniquely identify rows in a table.

Question 19

How is a Foreign Key different from a Primary Key?

Answer 19

A Primary Key is a key that uniquely identifies each record in a table, while a Foreign Key is a field in one table that refers to the Primary Key in another table. The Foreign Key establishes a link between the two tables, creating a relationship.

Question 20

Why is it important to ensure that there cannot be any duplicates in a relation?

Answer 20

It’s important to ensure that there cannot be any duplicates in a relation not just for the current state but also in principle. This ensures the uniqueness of each tuple and maintains the integrity of the data in the relational database.

Question 21

Is every relation guaranteed to have a key?

Answer 21

No, not every relation is guaranteed to have a key. In some cases, it might be necessary to invent artificial new attributes, like National Insurance (NI) numbers or ISBN numbers, to ensure all tuples will be unique.

Question 22

What is a Primary Key, and how is it determined?

Answer 22

A Primary Key is one of the candidate keys chosen by the Database (DB) designer. It is a minimal set of attributes that uniquely identifies each tuple in a table. The selection of a primary key is a crucial design decision.