G1_P1_ER model

1. In which step in the database design process is the ER model used?

• Requirements collection and analysis

• Logical design

• Conceptual design

• Physical design

Answer explanation

Answer: Conceptual design

ER model is used to identify the entities that will be included in the database and the relationships between them, and ensure that there is no conflict between the design and the requirements. This is a crucial step, a backbone for the whole database design process.

2. A/An ________ is a set of entities of the same type that share the same properties, or attributes.

• Entity set

• Entity

• Relationship set

• Entity type

Answer explanation

Answer: Entity set

Entity type is a category that a particular entity belongs to, along with other entities with similar behaviors. Meanwhile, an entity set refers to the set of all entities of a particular type at any point in time. All entities within a set have to be of the same entity type.

3. What distinguishes between strong and weak entity types?

• Entities of strong entity types are physically stronger than those of weak entity types.

• Strong entity types are of greater concern in the database system than weak entity types.

• Each entity of a strong entity type has a key attribute that can uniquely identify the entity within the entity set.

• None of the above.

Answer explanation

Answer: Key attributes

The crucial difference between strong and weak entity types is the existence of attributes with unique values, or the key attributes. These values alone are enough to identify any particular entity in an entire set (e.g. the student ID). Weak entities do not have these attributes, therefore they must be identified by being related to another entity.

4. Degree of a relationship _______.

• Describes the total number of participating entities

• Can only be no more than 3

• Describes the number of relationship instances

• Can be 1

Answer explanation

Answer: Can be 1

The degree of a relationship is the number of participating entity types, therefore, the number of individual entities, or the number of relationship instances does not matter. There is no constraint on the maximum degree a relationship can be. In the case of degree being 1, the relationship is unary, meaning only entities within the same type relate to each other.

5. Which of the following represents a multi-valued attribute?

• 
• 
• 
• 

Answer explanation

a. Key attribute

b. Derived attribute

c. Multi-valued attribute

d. Simple attribute

6. Which of the following attributes of an individual can have multiple values?

• SSN

• Date of birth

• Current location in coordinates

• None of the above

Answer explanation

Answer: None of the above

Both SSN (social security number) and date of birth are evidently single-valued. A person can only be at one exact location at a time, therefore, current location in coordinates is also single-valued.

7. A lecturer can teach some classes, but there is only one lecturer in charge of each class. If we use cardinality ratio to describe this lecturer-class relationship, where should the number “1” be?

• On the same side as CLASS

• On the same side as LECTURER

• In the middle, above the relationship notation

• In the middle, below the relationship notation

Answer explanation

Answer: On the same side as LECTURER

This is a many-to-one or one-to-many relationship, as many CLASS entities are mapped to any LECTURER entity. Therefore, the notation is 1:N for LECTURER : CLASS.