Question

A birthdate attribute would appear for many entity types – for example students, employees, children. What is a birthdate likely to be: key or non- key?

Short answer

A birthdate is likely to be a non-key attribute because it does not uniquely identify every record, as different entities can have the same birthdate.

Step-by-step solution

Identify attributes

Define what key and non-key attributes are. A key attribute is a unique identifier for a record in a database. However, a non-key attribute is a feature that does not uniquely identify a record.

Analyze the given attribute

In this case, the attribute is 'birthdate'. There are many possible scenarios where two or more students, employees, or children (entities in general) could share a birthdate. Therefore, a birthdate doesn't necessarily uniquely identify a record, as multiple entities can have the same birthdate.

Determine if birthdate is a key or non-key attribute

Considering there can be repetitions in the 'birthdate' attribute among entities and it doesn't uniquely identify every entity, the 'birthdate' attribute should be considered as a non-key attribute.

Key concepts

Entity Attributes

When designing a database, one of the essential steps is to identify the attributes of each entity. Attributes are characteristics or properties of an entity. For instance, if the entity is 'student', the attributes could include "name", "birthdate", and "student ID". Entity attributes help describe what kind of information we need to keep in the database regarding each entity. They provide meaningful data that can be used in different ways by users or by applications. Choosing the right attributes is crucial to ensuring that the database can meet user needs.
Entity attributes should reflect real-world data as closely as possible. In doing so, they enable the database to accurately represent the entities it is designed to store. Every attribute should have a reason for being in the database, ideally tied to the goals it is set to achieve.

Key Attributes

Key attributes are crucial when dealing with databases, as they are the unique identifiers for a record. For example, in a student database, the student ID is often a key attribute. That's because every student has a unique student ID to distinguish them from others. Key attributes ensure that each record can be uniquely identified among all others. This uniqueness is important for efficient data retrieval and management. It prevents duplication and maintains the integrity of the database structure. When selecting key attributes, it's essential to choose attributes that will always remain unique, such as social security numbers, if appropriate and permissible.
Key attributes also enable efficient indexing and querying. They play a critical role in normalizing the database, helping to avoid redundancy and ensuring consistency within the datasets.

Non-Key Attributes

Non-key attributes are equally important for describing an entity, but unlike key attributes, they do not uniquely identify a record. An example of a non-key attribute is 'birthdate'. While helpful for providing more information about an entity, 'birthdate' is not unique, as multiple entities, like different students or employees, might share the same birthdate. Non-key attributes add rich details and contextual information to the data. Although they are not used for identifying records, they are vital for understanding the entity's properties and for various analytical purposes. They allow users to query and sort data based on these descriptive facts. When deciding on non-key attributes, it is important to choose attributes that add significant value without overcrowding the database. They should enhance the usefulness of the data, supporting the objectives that the database is intended to achieve.