What is used to indicate a weak entity in an ERD?Double rectangular boxSingle rectangular boxDouble diamondSingle diamond

Step 1: Break Down the Problem

We need to identify the symbol that represents a weak entity in an Entity-Relationship Diagram (ERD) from the given options:

1. Double rectangular box
2. Single rectangular box
3. Double diamond
4. Single diamond

Step 2: Relevant Concepts

In ERD notation:

• A weak entity is an entity that cannot be uniquely identified by its attributes alone and relies on a "strong" or "owner" entity.
• Weak entities are represented using a specific symbol in ERDs to differentiate them from regular entities.

Step 3: Analysis and Detail

• Double Rectangular Box: This is the symbol used to represent a weak entity. It clearly indicates that this entity is dependent on another entity for its identification.
• Single Rectangular Box: This is typically used for regular entities.
• Double Diamond: This symbol usually represents a derived attribute.
• Single Diamond: This is employed to represent a regular attribute.

Step 4: Verify and Summarize

Based on standard ERD notation, the double rectangular box is indeed used to indicate a weak entity. Thus, from the options provided, the correct answer is clear and stands verified.

Final Answer

The correct indication of a weak entity in an ERD is a double rectangular box.