1Z0-006 Entity-Relationship Modeling 2 — Questions and Answers
Question 1: In an ER diagram, which symbol is used to represent a weak entity?
- Single rectangle
- Double rectangle (Correct answer)
- Diamond shape
- Ellipse
Correct answer: Double rectangle
A weak entity is depicted with a double rectangle to distinguish it from a regular (strong) entity.
Question 2: What is a 'discriminator' (partial key) in the context of weak entities?
- A foreign key that links two strong entities
- An attribute that uniquely identifies weak entity instances among those associated with the same owner entity (Correct answer)
- A derived attribute computed from other attributes
- A multivalued attribute stored in a separate table
Correct 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.
Question 3: Which relationship type links a weak entity to its owner entity in an ER diagram?
- Identifying relationship (Correct answer)
- Non-identifying relationship
- Recursive relationship
- Ternary relationship
Correct 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.
Question 4: A 'derived attribute' in an ER diagram is best described as:
- An attribute stored directly in the database
- An attribute whose value can be calculated from other stored attributes (Correct answer)
- A composite attribute made of multiple simple attributes
- A multivalued attribute with more than one value per entity
Correct 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.
Question 5: In an ER model, which of the following best describes a 'composite attribute'?
- An attribute that can hold multiple values simultaneously
- An attribute composed of several sub-attributes that together form a meaningful whole (Correct answer)
- An attribute whose value is calculated from other attributes
- An attribute that uniquely identifies every entity instance
Correct 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.
Question 6: When converting a ternary relationship to relational tables, the usual approach is to:
- Create a single table combining all three entities
- Create a separate junction (associative) table that holds the primary keys of all three participating entities (Correct answer)
- Ignore the relationship and link entities pairwise
- Add a foreign key to one of the three entity tables
Correct 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.
Question 7: Which notation style uses 'crow's foot' symbols to indicate cardinality on an ER diagram?
- Chen notation
- UML class diagram notation
- Crow's Foot (IE) notation (Correct answer)
- Bachman notation
Correct 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.
1Z0-006 Entity-Relationship Modeling 2
In an ER diagram, which symbol is used to represent a weak entity?