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Entity-Relationship Diagrams

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An Entity-Relationship Diagram (ERD) is a visual representation of the data entities within a system and the relationships between those entities. ERDs are fundamental tools in data modeling and analysis, used to depict the logical structure of databases. They help in illustrating the system's data…

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PMI-PBA - Entity-Relationship Diagrams Example Questions

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Question 1

When creating an Entity-Relationship Diagram (ERD), what is the purpose of a weak entity?

Correct Answer: An entity that cannot be uniquely identified by its own attributes and depends on another entity for identification

A weak entity in an ERD is an entity type that cannot exist on its own and relies on another (strong) entity for its identification. This concept is fundamental in database design. The correct answer accurately describes that weak entities require attributes from another entity to be uniquely identified. This is a key characteristic of weak entities in database modeling. The other options are incorrect because: - Having multiple primary keys is not related to weak entities - this is a misconception about composite keys - Optional attributes are unrelated to weak entities - they describe attribute properties, not entity dependencies - Derived attributes and cascading relationships are different concepts from weak entities - they deal with calculation rules and referential integrity respectively Weak entities are commonly used in real-world scenarios, such as modeling 'room numbers' in a building (rooms need the building for identification) or 'order items' in an order (items need the order for identification).

Question 2

In an Entity-Relationship Diagram (ERD), which cardinality constraint specifies that one instance of an entity must be associated with at least one instance of another entity?

Correct Answer: One-to-one mandatory relationship (1:1)

In ERD, a mandatory relationship (also known as total participation) indicates that each instance of an entity must participate in the relationship with another entity. The one-to-one mandatory relationship (1:1) is correct because it specifies that each instance of one entity must be associated with exactly one instance of another entity, and vice versa. The other options are incorrect because: - A one-to-many optional relationship with partial participation means some instances may not participate in the relationship - A many-to-many recursive relationship involves the same entity type relating to itself, which is not relevant to the question - A zero-to-many conditional relationship explicitly allows for no participation, contradicting the mandatory requirement stated in the question

Question 3

In an Entity-Relationship Diagram (ERD), what does a crow's foot notation between two entities represent?

Correct Answer: A many-to-one relationship between the entities

In Entity-Relationship Diagrams (ERD), a crow's foot notation represents a 'many' relationship on the side where the crow's foot appears. When connected to another entity, it specifically indicates a many-to-one relationship from the crow's foot side to the other entity. The other answers are incorrect because: Recursive relationships are shown by a relationship line that loops back to the same entity, not by a crow's foot. Mandatory dependencies are typically shown using different notation (such as solid vs. dashed lines), not crow's feet. One-to-one relationships are shown using simple line connections or different notation styles, never with crow's feet, as crow's feet specifically represent the 'many' side of a relationship.

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