Relational Model : MCQs & PYQs with Explanation

Option D

The attribute X is a composite attribute made up of three components, A1, A2, and A3, whose domain sizes are 5, 3, and 4 respectively. Since A2 is a multi-valued attribute, it can take multiple values from its domain or even be NULL.

If the domain of A2 has 3 elements, then the number of possible subsets of A2 is 23 = 8, because each element may be either included or not.
Now, the total number of possible combinations for X is calculated as:
Domain size of X = (Domain of A1) × (Domain of A2) × (Domain of A3)
Domain size of X = 5 × 8 × 4 = 160

Option B

In the relational model of DBMS, formal relational terms are often represented by informal table-related terms.

• A relation represents a complete table in a database.
• A tuple represents a single row or record in a table.
• An attribute represents a column or field in a table.
• A domain represents the set of permissible values that an attribute can hold.

Option A

A Relational Database Model stores data in the form of relations (tables). A relation consists of rows (tuples) and columns (attributes).
Each attribute in a relation has a domain. A domain is the set of all valid values that an attribute can take.
E.g.:

• Domain of Age = {18, 19, 20, ..., 50}
• Domain of Gender = {Male, Female, Other}
• Domain of Department = {CS, IT, EC, ME}

If a relation has N attributes, then each attribute has its own domain, represented as X₁, X₂, X₃, ..., Xₙ. The Cartesian Product of these domains, denoted by X₁ × X₂ × X₃ × ... × Xₙ, represents all possible combinations of values obtained by selecting one value from each domain. 
However, a database table does not store every possible combination. It stores only those combinations that are valid and meaningful according to the rules and constraints of the database. 
Therefore, a relation (table) is always a subset of the Cartesian Product of its domains.
Mathematically, if R represents a relation, then it is expressed as: R⊆X₁×X₂×X₃×⋯×X_N or Relation ⊆ Cartesian Product of Domains.

Option A

A Schema represents the overall logical structure of a database. It includes definitions of all tables, fields or attributes, data types, and relationships among the tables. The schema acts as a blueprint that describes how data is organized in the database.

Option A

In a database, an attribute represents a property or characteristic of an entity. The actual values stored for these attributes describe a particular entity.
For example, consider a Student entity with the attributes RollNo, Name, and Age. If the values are 101, Suresh Kulahry, 32, these attribute values describe a particular student entity.

• A Tuple represents a complete row or record in a relational table.
• A Field generally represents a column or attribute.
• A View is a virtual table created from one or more tables.

Option B

In a database, a field represents a single piece of data, such as a name or fees. When several related fields are combined together to describe a complete entity, they form a Record. For example, a student record may consist of fields like rollno, name, age, and course.

• An attribute refers to a property of an entity.
• A table is a collection of many records.

Option D

A Schema of a table defines the structure of the table, such as column names, data types, constraints, etc. This is not the actual data, but information about the data, which is called Metadata.

• Atomicity is a property of transactions (ACID).
• Entity represents a real-world object like student, employee.
• Relationship defines association between entities.

Option B

A Many-to-Many (M:N) relationship occurs when multiple records in one table are related to multiple records in another table. Such a relationship cannot be implemented directly in a relational database. To resolve this, an associative entity (junction table) is created.

THIS ASSOCIATIVE ENTITY:

• Breaks the M:N relationship into two 1:M relationships.
• Contains foreign keys from both tables.
• May also have its own attributes.

Option B

In the Relational Model, every attribute in a table must store a single, indivisible value. This means the model does not allow composite attributes, which can be divided into sub-parts, or multivalued attributes, which can hold more than one value at the same time. The type of rule that enforces this requirement is known as a Domain Constraint.

Domain constraints define what type of values an attribute (column) can store. They ensure that:

• Each attribute stores atomic values.
• No column can store multiple values.
• No column can contain a structured or composite value.

Thus, domain constraints automatically prevent composite and multivalued attributes.

Option A

In a relational database table, Cardinality refers to the total number of rows or records present in the table. It represents how many individual data entries the table holds.
The Degree refers to the total number of columns or attributes in the table, which describe the structure of each record.