Chapter 5 Flashcards
A data model is a plan for a database design.
True
The method of constructing data models used in the text is the extended entity-relationship (E-R) model.
True
An entity is something that users want to track.
True
Entities of a given type are grouped into entity classes.
True
An entity class is described by the structure of the entities in that class.
True
An entity instance is the occurrence of a particular entity.
True
An entity instance of an entity class is the representation of a particular entity and is described by the values of the attributes of the entity.
True
An identifier of an entity instance is one or more attributes that name or identify entity instances.
True
A compound identifier is an identifier consisting of two or more attributes.
False
In E-R modeling, an attribute describes the characteristics of an entity.
True
In E-R modeling, entities within an entity class may have different attributes.
False
An identifier of an entity instance must consist of one and only one attribute.
False
A composite identifier is defined as a composite attribute that is an identifier.
False
An identifier serves the same role for a table that a key does for an entity.
False
Entities can be associated with one another in relationships.
True
The degree of a relationship is the number of entity classes in the relationship.
True
A binary relationship is a relationship between two or more entities.
False
Relationships of degree two are referred to as binary relationships.
True
E-R modeling recognizes both relationship classes and relationship instances.
True
In today’s E-R models, attributes of relationships are still used.
False
A single relationship class involves only one entity class.
False
A binary relationship is a relationship based on numerical entity instance identifiers.
False
The degree of a relationship is expressed as the relationship’s maximum cardinality.
False
When transforming a data model into a relational design, relationships of all degrees are treated as combinations of binary relationships.
True
The principal difference between an entity and a table is that you can express a relationship between entities without using foreign keys.
True
When designing a database, first identify the entities, then determine the attributes, and finally create the relationships.
False
The notation 1:N shows the relationship’s maximum cardinality.
True
Relationships are classified by their cardinality.
True
A relationship’s maximum cardinality indicates the maximum number of entities that can participate in the relationship.
False
In an E-R model, the three types of maximum cardinality are 1:1, 1:N and N:M.
True
In a 1:N relationship, the term parent refers to the N side of the relationship.
False
In a 1:N relationship, the parent entity is on the one side of the relationship, and the child entity is on the many side of the relationship.
True
A relationship’s minimum cardinality indicates the number of entity instances that must participate in the relationship.
True
A relationship’s minimum cardinality indicates whether or not an entity must participate in the relationship.
True
In an E-R model, the three types of minimum cardinality are mandatory, optional and indeterminate.
False
An entity that represents something that can exist on its own is called a strong entity.
True
E-R models use an identifying relationship to connect entities that are ID-dependent.
True
An ID-dependent entity is an entity whose identifier includes the identifier of another entity.
True
ID-dependent entities are associated by a nonidentifying relationship.
False
A weak entity is an entity that cannot exist in the database without (and is logically dependent upon) another type of entity also existing in the database.
True
) ID-dependent entities are a common type of weak entity.
True
All weak entities must have a minimum cardinality of 1 on the entity on which it depends.
True
Subtype entities contain only attributes unique to the subtypes.
True
An attribute that determines which subtype is appropriate is called a discriminator.
True
An exclusive subtype pattern has one supertype entity that relates to one or more subtype entities.
False
Entities with an IS-A relationship should have the same identifier.
True
One example of a database design using an ID-dependent relationship is the association pattern.
True
One example of a database design using a strong relationship is the multivalued attribute pattern.
False
One example of a database design using an ID-dependent relationship is the archetype/instance pattern.
True
Data modelers agree that weak, non-ID-dependent entities exist and are important.
False
Entities containing optional sets of attributes are often represented using subtypes.
False
The supremetype entity contains the attributes that are common to all subtypes.
False
An attribute that determines which subtype is appropriate is called a discriminator.
True
Subtypes can be exclusive or inclusive.
True
Relationships between supertypes and subtypes are called IS-A relationships.
True
Relationships among instances of a single entity class are called redundant relationships.
False
There are three types of recursive relationships: 1:1, 1:N and N:M.
True
Recursive relationships only exist for one-to-one relationships.
False
