Warning: Illegal string offset 'id' in /home/upanswer/public_html/wp-content/plugins/content-locker/includes/class-cl-site-front.php on line 99
August 2018 - UpAnswers.Com (Homework Help)
Breaking News

Monthly Archives: August 2018

(21) Discuss the difference between existence dependency and identification dependency?

Question:

Discuss the difference between existence dependency and identification dependency?

 

SOLUTION

Total participation of an entity type in a relationship type is defined as existence dependency. Identification dependency is existence dependency where a weak entity type is always dependent on the unique identifier of its identifying parent for its unique identification.

(19) Why can total participation of an entity type in a relationship type also be referred to as existence dependency of that entity type in that relationship type?

QUESTION:

Why can total participation of an entity type in a relationship type also be referred to as existence dependency of that entity type in that relationship type?

 

SOLUTION

Total participation occurs if, in order to exist, an entity type must participate in the relationship. Thus, total participation of an entity type in a relationship type can be termed existence dependency of that entity type in that relationship type.

(14) What is the value of using role names to describe the participation of an entity type in a relationship type?

QUESTION:

What is the value of using role names to describe the participation of an entity type in a relationship type?

 

SOLUTION

Role names can be used to clarify the nature of the participation of each entity type involved in a relationship type. They can be particularly helpful in clarifying the nature of the structural constraints in a recursive relationship.

(12) What is a relationship type? How does a relationship type differ from a relationship instance?

QUESTION:

What is a relationship type? How does a relationship type differ from a relationship instance?

 

SOLUTION

A relationship type is a meaningful association among entity types. A relationship instance is an occurrence of a relationship type.

(11) Give an example of three entity types and accompanying attributes that might be associated with a database for a car rental agency?

QUESTION:

Give an example of three entity types and accompanying attributes that might be associated with a database for a car rental agency?

 

SOLUTION

VEHICLE (VehicleID, LicensePlate#, Make, Model, Year, Mileage, …)

RENTER (License#, Name, Address, City, State, Zipcode, Insurance, etc.)

VEHICLE_RENTAL (VehicleID, License#, Dateout, Datein, Mileageout, Mileagein)