Entity-Relationship Modeling Flashcards

In an ER diagram, which symbol is used to represent a weak entity?

Answer: Double rectangle

A weak entity is depicted with a double rectangle to distinguish it from a regular (strong) entity.

What is a 'discriminator' (partial key) in the context of weak entities?

Answer: An attribute that uniquely identifies weak entity instances among those associated with the same owner entity

A discriminator, or partial key, distinguishes weak entity instances that belong to the same strong (owner) entity.

Which relationship type links a weak entity to its owner entity in an ER diagram?

Answer: Identifying relationship

An identifying relationship (drawn as a double diamond) connects a weak entity to its owner entity, providing the context needed for identification.

A 'derived attribute' in an ER diagram is best described as:

Answer: An attribute whose value can be calculated from other stored attributes

Derived attributes, shown with a dashed ellipse, are computed at query time from other attributes rather than stored persistently.

In an ER model, which of the following best describes a 'composite attribute'?

Answer: An attribute composed of several sub-attributes that together form a meaningful whole

A composite attribute is divided into smaller sub-parts, such as 'Full Name' broken into First Name, Middle Name, and Last Name.

When converting a ternary relationship to relational tables, the usual approach is to:

Answer: Create a separate junction (associative) table that holds the primary keys of all three participating entities

A ternary relationship is typically mapped to an associative table whose primary key is a composite of the three participating entity keys.

Which notation style uses 'crow's foot' symbols to indicate cardinality on an ER diagram?

Answer: Crow's Foot (IE) notation

Crow's Foot (also called Information Engineering notation) uses a crow's foot symbol to denote the 'many' side of a relationship.