1Z0-006 Entity-Relationship Modeling 4 — Questions and Answers
Question 1: In EER (Enhanced Entity-Relationship) modeling, 'specialization' is best defined as:
- Combining multiple entity types into a single superclass
- Defining subclasses of an entity type based on distinguishing characteristics (Correct answer)
- Merging attributes from two entities into one
- Creating a relationship between two different database schemas
Correct answer: Defining subclasses of an entity type based on distinguishing characteristics
Specialization is a top-down process of defining subclasses from a superclass based on specific distinguishing features.
Question 2: What is 'generalization' in EER modeling?
- Breaking a single entity into multiple subclasses
- Combining common attributes of multiple entity types into a higher-level superclass (Correct answer)
- Assigning foreign keys to enforce relationships
- Defining a total participation constraint on a subclass
Correct answer: Combining common attributes of multiple entity types into a higher-level superclass
Generalization is a bottom-up process where shared attributes of multiple entity types are abstracted into a common superclass.
Question 3: A 'disjoint' specialization constraint in EER means:
- An entity instance can belong to more than one subclass simultaneously
- An entity instance can belong to at most one subclass at a time (Correct answer)
- All entity instances must belong to at least one subclass
- No entity instance can belong to any subclass
Correct answer: An entity instance can belong to at most one subclass at a time
A disjoint constraint (marked 'd' in EER diagrams) means the subclasses are mutually exclusive — an entity can be in only one subclass.
Question 4: In EER, an 'overlapping' specialization means:
- Subclasses share the same primary key
- An entity instance can simultaneously belong to more than one subclass (Correct answer)
- The superclass has no attributes of its own
- All subclass instances must also appear in another subclass
Correct answer: An entity instance can simultaneously belong to more than one subclass
An overlapping constraint (marked 'o') allows an entity instance to be a member of multiple subclasses at the same time.
Question 5: Which of the following best describes 'total specialization'?
- Every superclass instance must belong to at least one subclass (Correct answer)
- Subclasses are mutually exclusive
- Every subclass must have a discriminating attribute
- The superclass cannot have its own instances
Correct answer: Every superclass instance must belong to at least one subclass
Total specialization (double line in EER) means every entity in the superclass must also be a member of at least one subclass.
Question 6: An 'associative entity' (also called a gerund) is used in ER modeling to:
- Replace a weak entity with a stronger one
- Treat a many-to-many relationship as an entity so it can have its own attributes and participate in other relationships (Correct answer)
- Define the cardinality of a one-to-one relationship
- Convert a multivalued attribute into a separate table
Correct answer: Treat a many-to-many relationship as an entity so it can have its own attributes and participate in other relationships
An associative entity 'reifies' a relationship, turning it into an entity that can carry its own attributes and connect to other entities.
Question 7: Which mapping rule is used when converting a 1:1 relationship to relational tables?
- Create a separate junction table for the relationship
- Add the primary key of either participating entity as a foreign key in the other entity's table (Correct answer)
- Merge both entities into one single table always
- Add foreign keys to both entity tables pointing to each other
Correct answer: Add the primary key of either participating entity as a foreign key in the other entity's table
For a 1:1 relationship, the standard approach is to add the primary key of one entity as a foreign key in the other entity's table, preferably on the total-participation side.
1Z0-006 Entity-Relationship Modeling 4
In EER (Enhanced Entity-Relationship) modeling, 'specialization' is best defined as: