Please answer all the questions blew with short answers, thank you so much. 1. W
ID: 3753995 • Letter: P
Question
Please answer all the questions blew with short answers, thank you so much.
1. When designing an ERD , what is meant by a weak relationship? Provide an example of such a relationship.
2. Explain multivalued attributes with the help of examples. How are multivalued attributes indicated in the Chen Entity Relationship model?
3.
List five generic aggregate functions that can be used with the following data. Comment on their usefulness in describing the data.
Table: tblSales
index
month
sales
1
July
$16,000
2
August
$17,280
3
September
$23,660
4
October
$17,493
5
November
$28,805
6
December
$32,470
4. What is a ternary relationship? Provide some business rules examples that specify the need for a ternary or higher - order relationship.
5.
Visit the home page of the Barnes and Noble Web site and examine especially the links towards the bottom portion of the page.
https://www.barnesandnoble.com
Then choose one of these categories, such as Shipping Rates or B&N Membership, and discuss how database management plays a role in connecting the Web site with the customers of the company.
Table: tblSales
index
month
sales
1
July
$16,000
2
August
$17,280
3
September
$23,660
4
October
$17,493
5
November
$28,805
6
December
$32,470
Explanation / Answer
We are allowed to answer only four sub parts.
1) Weak relationship:
An entity which can't exist without parent entity is called weak entity. Relationship between parent and weak child is called weak realtionship.
Room doesn't exist without a building. So Room is a weak entity wheras building is a strong entity.
2) Multivalued Attributes:
Multivalued attribute can have more than one value for an attribute. Hobbies of a person can be multiple.
It is denoted by double border ellipse.
3)
1) AVG - avg sales of the second half of the year in the table
2) SUM - Total sales for the table
3) MAX - Maximum sale value
4) MIN - Min sale value
5) COUNT - number of rows in the table
4) Ternary relationship:
Relationship between three entities.
Let's consider Patient, Treatment, Doctor are three entities. Patient consults Doctor for a treatment. This is the ternary relationship between the entities.
To understand the relationship between more than two entities, N-ary relationships are used. One of them is ternary relationship which depicts relationship between three entities.
In case of any doubts, please comment.