Question

Define the following terms: entity, attribute, attribute value, relationship instance, composite attribute, multivalued attribute, derived attribute, complex attribute, key attribute, value set (domain).

Short answer

These terms are related to the concept of Entity-Relationship Model (ER Model) in database systems. Entity is an existing object in reality, attribute is a characteristic, and attribute value is the corresponding value. Relationship instance links entities. A composite attribute can be divided into sub-attributes, while a multivalued attribute can hold multiple values. A derived attribute is calculated from other attributes. A complex attribute can be composite, multivalued or derived. A key attribute uniquely defines an entity and a value set (domain) is the set of possible values for an attribute.

Step-by-step solution

Definition of Entity

An entity is a thing in the real world with an independent existence. It can be a physical object or a conceptual idea which can be identified uniquely.

Definition of Attribute

An attribute is a property or a characteristic of an entity. It describes the features of the entity.

Definition of Attribute Value

Attribute value is the particular value that an attribute can hold. The values can be numerical or textual.

Definition of Relationship Instance

A relationship instance is an association of entities. It is the occurrence of linked entities.

Definition of Composite Attribute

A composite attribute is an attribute that can be divided into other attributes. For example, Address can be divided into Street, City, State, Country, etc.

Definition of Multivalued Attribute

A multivalued attribute can hold multiple values. For example, a person's phone number is a multivalued attribute as a person may have more than one phone number.

Definition of Derived Attribute

A derived attribute is an attribute whose value is calculated from other attributes. For example, age can be derived from date of birth.

Definition of Complex Attribute

A complex attribute is an attribute that can have composite and multivalued attributes or it could be derived.

Definition of Key Attribute

A key attribute is an attribute whose value can be used to uniquely identify an entity. For example, student number in a university can be a key attribute.

Definition of Value Set (Domain)

A value set, also known as domain, is the set of values that an attribute can take. For example, for a gender attribute, the domain can be {Male, Female}.

Key concepts

Attributes

Attributes are the defining elements of an entity in a database. They describe how an entity appears or behaves. For example, if we consider a 'Student' entity, attributes may include name, age, and student ID. Each attribute represents a characteristic of the entity. Attributes help in understanding and identifying different entities through their specific values.

• They can have quantitative values, like numbers (age: 20), or qualitative values, like text (name: "John").
• An entity might have many attributes, and each of them provides indispensable information about the entity.

In summary, attributes play a crucial role in differentiating and detailing each entity within the entity-relationship model.

Key Attribute

A key attribute is vital in identifying each entity uniquely. It is an attribute that helps in distinguishing one entity from another entity in a set. Think of it like a unique fingerprint for each entity.
For instance, a student number in a university can serve as a key attribute because it is unique to each student. No two students can have the same student number.

• Key attributes are often used as identifiers in databases.
• They ensure that each record in the database is distinct and can be retrieved accurately.

Choosing the right key attribute is crucial as it affects the organization's ability to structure and access database information efficiently.

Value Set

The value set, often referred to as a domain, encompasses all possible values that an attribute can have. It acts like a boundary that defines what an attribute's values might be. For example, the value set for a gender attribute might be {Male, Female}.

• Value sets provide a consistent framework for understanding what values are acceptable for an attribute.
• They ensure data integrity by restricting the attribute's values to a predefined list.

A well-defined value set helps maintain the data accuracy and integrity within a database, making operations like querying and data manipulation more efficient and error-free.

Relationship Instance

A relationship instance reveals how entities are associated with one another in a database. It depicts a specific occurrence of a connection between two or more entities.
For example, if we have two entities, 'Student' and 'Course', a relationship instance might be 'Enrollment'. This represents a student's enrollment in a course.

• Relationship instances make it possible to illustrate connections between distinct entities.
• They can be directional, indicating the flow or direction of the relationship.

Through relationship instances, databases can simulate and query real-world relationships, offering more meaningful data analysis.