In this case will the employee have the information about the rental date, so as to send a reminder? If not, how do I execute the connection?
Make the diagram like this to show that the employee is given information about the rents. Information about the attributes of the rents relationship is shared between the customer entity and the employee entity.
This diagram could be made more detailed if more information about the database is provided, especially if the information is in the form of code.
Related
My Entity Relationship Diagram
My ER diagram designed for the Orders database about customers and their orders for
a company. Each item
in the database must have an “owning” salesman, whether or not it is being ordered.
With that being said I was wondering whether there were any issues with my diagram? What do you suggest I should change?
Should I remove the customer and salesman attributes?
I not sure but I think in your the Address Entity is extra its a attribute customer only so why you create address as a separate attribute.
Please refer the attach image to correct your different relationship with attributes.
Have a simple question, but I think I am overthinking it. I need to make an E/R diagram out of this:
Substantial fees are due every calendar year. Fee payments must be
made via a bank transfer, mentioning the member number and the
membership year it applies to. The database should store the date of
payment.
I am ignoring calendar year, as I think it is not relevant for the E/R diagram. I have an entity called "Members" which I like to "Fee" via *"payed via the relationship (diamond symbol) a bank transfer"*.
Now, my question is: should "member number" and "membership" be part of the "fee" entity or the "member" entity? Or both? Because I am thinking to add a new relationship to "fee" giving it the name "consists of" and then link "member number" and "membership", but I don't know whether that's good or not.
And what to do with the last sentence? "The database should store the date of payment."? Can I ignore it?
From your description I got:
You have entity sets Members and Payments
Members are identified by a member_number
Payments have attributes date, amount and membership_year
Obviously, we also need:
Payments have an attribute amount
How are we going to identify Payments? No combination of the listed attributes are uniquely identifying in my opinion. A Member could make two identical Payments on the same date with the same amount, for the same membership year, e.g. if they accidentally only paid half of the annual fee at first then made a second payment to correct.
Let's introduce a surrogate key:
Payments are identified by a payment_id
We also need a relationship between the two entity sets:
Each Payment is associated with a single Member
Each Member can make multiple Payments
We can put this info into an ER diagram:
To derive a table diagram, Chen's original method implemented every entity relation (entity key and attributes) and relationship relation (relationship keys (i.e. related entity keys) and relationship attributes) as separate tables:
However, it's common practice to denormalize tables with the same primary key:
I recommend you study Chen's paper The Entity-Relationship Model - Toward a Unified View of Data. Codd's paper A Relational Model of Data for Large Shared Databanks provides valuable background.
First I'll explain the statement of diagram and after that I will explain my problem and I'll attach my actual diagram.
I should make an ER diagram about the following statement:
Perform the design and implementation of a database to store information about patients admitted to a hospital, patients can be adults or children. In the case of children we save information from who their parents who in turn can also be patient. In this hospital, patients arriving at the emergency department of the hospital are examined by a doctor and, depending on their health status, are entered in the corresponding plant (traumatology, intensive care...) under the supervision of a nurse.
Each patient receives a treatment that must be stored
Well, I design the following diagram; but my main problem is how to make the relation between fathers that can be patients. I decided put all fathers as patients and don't represent adults as entity, I have considered them implicit into patient's entity. But I'm not very sure about the validity of my solution.
I'd be grateful if someone can help me with my doubt.
How about subtyping patient from person and then creating a relationship from patients who are children to their parent persons? In this way, not every person need to be a patient but parents can be patients too. The relationship between parent and child indicates the role of each so there's no need to specifically subtype patients into parents or children.
Note also that your Doctors can currently only examine one patient.
So I have some question about the association, aggregation and composition in UML diagram. Here is some scenarios :
Product review rating composition to product review. This means that for each product review rating MUST HAVE product review? If product review doesn't exist, rating for review doesn't make sense.
Customer NRIC associate to cart and order. We cannot use aggregation because if customer does not exist, cart and order cannot exist also.
Can somebody please help me check if my relationships are correct? Is it good to link all your tables with association because I kind of confused on aggregation and association. I do not know when to use that.
Correct me if I am wrong. Thanks in advance.
Take a look at this class diagram example for composition:
Composition declares an ownership associationship. Person owns Leg and Hand. Or other way around, Hand belongs to Person.
Now ask yourself how would you describe each relationship in your model. If you would say Product review rate owns a Product review or Product review belongs to a Product review rate, then your diagram is OK. If the ownership has the opposite direction (Product review rate belongs to Product review, then the diamond must go to the other side of the association.
The same thing applies to aggregation. If the association somehow declares an ownership, then the diamond must go to the side of the owner class.
The difference between aggregation and composition is that objects owned as composites can't be created without their owner, so usually they are created by their owner. These objects are destroyed when their owner is destroyed, they couldn't be used by another owner after their owner dies. Objects owned by an aggregation association can be created without their owner and possibly could outlive him and serve another owner.
I am trying to think of the best design for trainers and clients database.
My initial thought was this:
Entity person with common attributes of clients and trainers (name, dob, etc.). A client can have only one trainer. One trainer can have many clients.
I wonder whether creating an entity user for controlling clients and trainers privileges, or just adding an attribute Role in person
Another thing I had considered was having everything in a single entity with a recursive relationship?
Any suggestion?
Thanks.
Trainers and Clients from an entity perspective probably have different data that you care to track about each one. You can still have a global users table, but the trainer and client should have a 1:1 relationship with the user entity. You can then have a join table between clients and trainers. I would suggest a many to many relationship here, just in case someone really wants to get in shape and wants to have 2 trainers.
Can trainers have trainers? For example, a trainer who specializes in triathletes might be a weak swimmer and have a swim coach.
I like the Role design myself.