In database design, what is meant by a composite attribute in an entity–relationship (ER) model?

Introduction / Context:
When designing a database using an entity–relationship (ER) model, attributes describe properties of entities, such as a person or a product. Attributes can be simple, composite, single valued, multivalued, and so on. Understanding the difference between simple and composite attributes is important because it influences how you normalize the design and eventually create tables in a relational database.

Given Data / Assumptions:

• The question is about ER modeling concepts used in logical database design.
• We are specifically concerned with the definition of a composite attribute.
• We assume that the learner knows what a basic attribute and an entity are.

Concept / Approach:
A simple attribute is atomic and cannot be split into smaller meaningful pieces. In contrast, a composite attribute can be logically divided into several component attributes that still have meaning. A classic example is a full name attribute that can be divided into first name, middle name, and last name. Another example is an address that can be split into street, city, state, and postal code. The key idea is that the overall attribute is made up of multiple subparts which may be stored separately in relational tables.

Step-by-Step Solution:
Step 1: Recall that in ER modeling, attributes can be simple or composite.Step 2: A simple attribute cannot be further divided into meaningful subparts, such as age or salary.Step 3: A composite attribute can be broken down into smaller attributes, such as address into city, state, and postal code.Step 4: Match this definition with the given options and select the one that clearly states that the attribute can be broken into components.

Verification / Alternative check:
If you think of how a logical ER diagram is converted into relational tables, composite attributes are often split into their components during table creation. For example, instead of having a single column called full_address, designers may create separate columns for door_number, street_name, city, state, and pin_code. This conversion process reinforces that a composite attribute is something that naturally breaks down into smaller parts.

Why Other Options Are Wrong:
Option B: Describes a simple or atomic attribute, not a composite attribute.Option C: Talks about attributes belonging to unrelated entities, which is not a standard ER modeling concept for composite attributes.Option D: Refers to identificational attributes such as primary keys, which are not the same thing as composite attributes. A primary key can be simple or composite, but that is a different idea.

Common Pitfalls:
Learners sometimes confuse composite attributes with composite keys. A composite key is a combination of two or more attributes used together to uniquely identify an entity. A composite attribute, however, is a single logical property that has multiple subcomponents. Another mistake is thinking that any attribute with multiple values is composite. Multivalued attributes store multiple values of the same type, such as multiple phone numbers, whereas composite attributes group related subattributes into one logical attribute.

Final Answer:
The correct answer is An attribute that can be broken down into smaller component attributes.