Thread: ER designing.
01-31-06, 07:05 #1Registered User
- Join Date
- Jan 2006
I’ve three questions, would someone answer them please,
I have 3 entities:
The book entity(BookNo,BookNmae,AuthorName,Price...etc), the MembershipCard entity(CardNo,MembershipNo,ClientNo,PublishDate,Em pNo..etc), and the Client entity(ClientNo,ClientName,ClientAddr,ClientPhoneB ookNo,RequiredBookNo,..etc)
1-What is the relationship degree between them, is it ternary or binary?and Why?I'm so confused ,my answer is ternary, I made a (1:m) relationship between the clients entity and the books entity (a client may buy more than one book), (1:m) relationship between the employee entity and the books entity (an employee may sell more than one book)and a (1:m) relationship between the employee and the Client(an employee may serve more than one client(is it right or it's (M:N)).
So is my answer is right or wrong, please help me to understand, I’m so confused.
2- Is the cardinality degree between the Client entity and the book entity , (0,N) for the client entity and (1:N) for the book entity??
3-What is the best model to use in designing data in general,Chen's model or Crow's Foot and why?I think it's Crow's one ,for it's more arranged and easy to read.
Last edited by bright_moon; 01-31-06 at 08:00.
01-31-06, 10:00 #2Registered User
- Join Date
- Jan 2003
Never went to school for this myself, so I have to ask a question or two. What is the definition of Ternary and Binary in this context? Do you have an example?
01-31-06, 22:08 #3Annie's Dog Walker
- Join Date
- Nov 2004
- on the wrong server
No comp sci degree here either, but...
Can a client be served by more than one employee?
BTW, almost no one speaks of chen or crow or even cardinality in the commercial software world. How is school this semester? Any hot girls on the hall?
To do it all over again... I would have majored in business so I could go out and party every night and still be on the deans list.If one brings so much courage to this world the world has to kill them or break them, so of course it kills them. The world breaks every one and afterward many are strong at the broken places. But those that will not break it kills. It kills the very good and the very gentle and the very brave impartially. If you are none of these you can be sure it will kill you too but there will be no special hurry. Earnest Hemingway, A Farewell To Arms.