ERD shapes and meanings In a standard Chen-style ER diagram, what does a rectangle represent?

Introduction / Context:
Visual consistency in ER diagrams enables fast comprehension by diverse audiences. The rectangle, diamond, and oval are the three primary symbols in Chen notation. Correctly identifying them ensures that readers interpret the structure and constraints accurately when reviewing models or documentation.

Given Data / Assumptions:

• Notation: classic Chen ER modeling.
• Key symbols: rectangle (entity), diamond (relationship), oval (attribute).
• Specialized notations for subtypes or constraints may add more symbols but do not change these basics.

Concept / Approach:

An entity represents a distinguishable thing or concept about which the organization stores information, such as Customer, Product, or Invoice. In Chen notation, entities are shown as rectangles labeled with their names, typically singular nouns. Attributes connect to entities with ovals, and relationships among entities are depicted with diamonds and connecting lines annotated with cardinalities and participation constraints.

Step-by-Step Solution:

Verification / Alternative check:

Standard ER references and teaching materials consistently assign rectangles to entities in Chen notation. Crow’s foot notation also uses box-like shapes to represent entity types with attributes listed inside the box.

Why Other Options Are Wrong:

• Attribute: drawn as an oval.
• Optional participation: indicated via cardinality/participation markers, not a rectangle.
• Relationship: drawn as a diamond.
• Subtype: often shown with a specialized notation (for example, ISA) rather than a plain rectangle.

Common Pitfalls:

• Confusing the entity symbol with tables in physical design; the mapping is common but not one-to-one when normalization or denormalization is applied.

Final Answer:

Entity