A double ellipse represents _______ attribute in ER-diagram.

Question

Accepted Answer

The correct option is (1):
The correct symbol used in an Entity-Relationship (ER) diagram to represent a **Multi-valued** attribute is the **double ellipse** or double oval. A multi-valued attribute is a property that can hold multiple distinct values for a single entity instance at any given time. For example, if an entity like a 'Student' can have multiple entries for the 'Phone Number' attribute, it is considered multi-valued. The double ellipse notation visually conveys the fact that there is a one-to-many relationship between the single entity and its multiple attribute values. This is a critical distinction in database design, as it indicates that the attribute's values will typically be stored in a separate, linked table in a normalized relational database.

The incorrect option is (2):
**Composite** attributes are not represented by a double ellipse, but rather by a single ellipse that is connected to a set of smaller, component ellipses. A composite attribute is one that can be logically divided into smaller, meaningful sub-attributes. A classic example is the 'Address' attribute, which is composed of 'Street', 'City', and 'Zip Code' sub-attributes. Each of these sub-attributes would be an individual ellipse branching out from the main 'Address' ellipse. Therefore, the double ellipse is used to denote multiplicity of values, not a structural breakdown into constituent parts.

The incorrect option is (3):
**Derived** attributes are represented by a **dashed** or **dotted ellipse** in a standard ER diagram. A derived attribute is an attribute whose value is not explicitly stored in the database but can be calculated or computed from the values of other stored attributes. A clear example is the 'Age' attribute, which is not stored directly but is calculated from the 'Date of Birth' attribute and the current date. The dotted line symbolizes that the attribute's value is computational and transient, which is a fundamentally different concept and notation from the double ellipse for multiple values.

The incorrect option is (4):
**Complex** is not a formally defined, distinct attribute type in the standard Entity-Relationship model that is assigned a unique, dedicated graphical notation like the double ellipse. While an attribute can certainly exhibit 'complex' characteristics, such as being both multi-valued *and* composite, this complexity is represented by combining the standard notations. For instance, a complex attribute would use a double ellipse (for multi-valued) that then connects to smaller ellipses (for composite components). There is no single, unique symbol that stands only for 'Complex' attribute.