Chapter 4 Questions Group 8: Ifeanyichukwu Iwelunmor, Erika McClinton, Saurav Sharma Questions 1. What two conditions must be met before an entity can be classified as a weak entity? Give an example of a weak entity. For an entity to be considered a weak entity it must be existence-dependent on its parent entity and it must inherit at least part of its primary key from its paren
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Chapter 4 Questions
Group 8: Ifeanyichukwu Iwelunmor, Erika McClinton, Saurav Sharma
Questions
1. What two conditions must be met before an entity can be classified as a weak entity? Give an example of a weak entity.
For an entity to be considered a weak entity it must be existence-dependent on its parent entity and it must inherit at least part of its primary key from its parent entity. An example of a weak entity would be a bedroom in a house. Without being contained by the house it is not a bedroom.
5. Suppose you are working within the framework of the conceptual model in Figure Q4.5.
Figure Q4.5 The Conceptual Model for Question 5
Given the conceptual model in Figure Q4.5:
a. Write the business rules that are reflected in it.
1. A customer can own many cars.
2. Some customers do not own cars.
3. A car is owned by one and only one customer.
4. A car may generate one or more maintenance records.
5. Each maintenance record is generated by one and only one car.
6. Some cars have not (yet) generated a maintenance procedure.
7. Each maintenance procedure can use many parts.
8. A part may be used in many maintenance records.
9. Each maintenance procedure generates one or more maintenance lines.
10. Each part may appear in many maintenance lines.
b. Identify all of the cardinalities.
(these need to be put next to II and O<….in order from first to last) 1). (0,N)
2). (1,1)
3). (0,N)
4). (1,1)
5). (1,N)
6). (1,1)
7). (0,1)
8). (0,N)
7. How would you (graphically) identify each of the following ERM components in a Crow’s Foot model?
An entity would be represented by a rectangle containing the name of the entity. A cardinality would be showed through the use of Crow’s Foot symbols (i.e. two vertical dashes, two tilted dashes with vertical lines or open circle, etc.). A weak relationship would be indicated by a dashed line and a strong relationship would be indicated by a solid line.
21. The local city youth league needs a database system to help track children that sign up to play soccer. Data needs to be kept on each team and the children that will be playing on each team and their parents. Also, data needs to be kept on the coaches for each team. Draw the ERD with foreign keys for model described below.
Entities required: Team, Player, Coach, and Parent.
Attributes required:
Team: Team ID number, Team name, and Team colors.
Player: Player ID number, Player first name, Player last name, and Player age.
Coach: Coach ID number, Coach first name, Coach last name, and Coach home phone number. Parent: Parent ID number, Parent last name, Parent first name, Home phone number, and Home Address (Street, City, State, and ZIP Code).
The following relationships must be defined:
• Team is related to Player.
• Team is related to Coach.
• Player is related to Parent.
Connectivities and participations are defined as follows:
• A Team may or may not have a Player.
• A Player must have a Team.
• A Team may have many Players.
• A Player has only one Team.
• A Team may or may not have a Coach.
• A Coach must have a Team.
• A Team may have many Coaches.
• A Coach has only one Team.
• A Player must have a Parent.
• A Parent must have a Player.
• A Player may have many Parents.
• A Parent may have many Players.
| | Parent | PK | Parent_ID
registers
Problems
1. Use the following business rules to create a Crow’s Foot ERD. Write all appropriate connectivities and cardinalities in the ERD.
a. A department employs many employees, but each employee is employed by one department.
b. Some employees, known as “rovers,” are not assigned to any department.
c. A division operates many departments, but each department is operated by one division.
d. An employee may be assigned many projects, and a project may have many employees assigned to it.
e. A project must have at least one employee assigned to it.
f. One of the employees manages each department, and each department is managed by only one employee.
g. One of the employees runs each division, and each division is run by only one employee.
