Which of the following is a composite attribute?

A composite attribute is an attribute that can be decomposed into two or more smaller sub-attributes, each of which carries independent meaning of its own; ER modeling uses a composite attribute whenever a value is more usefully represented as a group of related simple attributes rather than one indivisible value. A simple (atomic) attribute, by contrast, cannot be meaningfully broken down any further — it is stored and interpreted as a single indivisible value.

Date-of-birth naturally decomposes into three independently meaningful sub-parts — day, month, and year — each of which can be validated, compared, or queried on its own (for example, filtering all employees born in a particular month). This structural decomposability is exactly the defining test for a composite attribute, so Date-of-birth is the composite attribute among the given options.

• Age represents a single numeric quantity (years elapsed since birth) with no independently meaningful sub-parts, so it is atomic; in fact, Age is more typically modelled as a derived attribute (computed from Date-of-birth) than as a composite one.

• Grade represents a single categorical value (e.g., A, B, C); it cannot be decomposed into further independently meaningful parts, so it is atomic.

• City represents a single place name; on its own it is atomic, though it may itself be one component of a larger composite Address attribute (together with street and state) in a fuller schema.

Re-applying the same decomposability test — does the value split into parts that are each independently useful? — only Date-of-birth (day, month, year) satisfies it among the four options, confirming Date-of-birth as the composite attribute.