Member Avatar for bangor_boy

Need some help, practising for an exam and need to make sure I have got this right as it has came up a number of times. Here is the information from a relational representation and I have drawn a ER diagram for this, can someone please tell me if I have got this right or where I have went wrong.

Thanks

model Engineering Company

relation Staff
StaffNo: StaffNumbers
Name: Names
Grade: Grades
AppointmentDate: Dates
primary key StaffNo

relation CompanyProject
ProjectId: ProjectIds
StartDate: Dates
EstimatedFinishDate: Dates
Manager: StaffNumbers
primary key ProjectId
alternate key Manager
foreign key Manager references Staff
constraint ((project CompanyProject over ProjectId) difference
(project WorksOn over ProjectId)) is empty
constraint (( project CompanyProject over ProjectId) difference
( project Machine over ProjectId)) is empty

relation WorksOn
ProjectId: ProjectIds
StaffNo: StaffNumbers
primary key (ProjectId, StaffNo)
foreign key ProjectId references CompanyProject
foreign key StaffNo references Staff

relation Machine
MachineId: MachineIds
Description: Descriptions
DateOfLastService: Dates
ProjectId: ProjectIds
primary key MachineId
foreign key ProjectId ** references** CompanyProject

relation MachineTraining
MachineId: MachineIds
StaffNo: StaffNumbers
DateOfTraining: Dates
primary key(MachineId, StaffNo)
foreign key MachineId references Machine
foreign key StaffNo references Staff

ERDIAGRAM.jpg 15.14 KB
Edited by bangor_boy
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Member Avatar for seslie

Hi bangor boy,

The relationship could be

one/many staff can work on one/many company projects
one staff can manage one project at a time

Depends on what u term as 'machine',

one/many company projects may be accessible via one/many machines or
one/many company projects may be worked on via one machine per staff
i.e one staff works on one machine

I don't really understand 'machine training' what's that supposed to be?

To enable us answer this question properly though, you might need to supply the problem statement, that's the main question.

Member Avatar for bangor_boy

I am afraid not much of a question to give more detail, I assume machine training is there so if you dont have the training you cant use the machine.

Give an E–R diagram and entity types that correspond to this relational
representation.

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