I have a question regarding ER diagram
The question is how do we connect entities in an ER diagram
the options are
1. foreign key
2. relationship
3. primarykey
4. association
I know if the question was about relational diagram the answer will be: FK, but as I recall there is no FK in ER diagram and the book says the right answer is 1, so any help?
Related
1.Several students from different departments may participate one project. Each project has at least one student member.
2.Each student may or may not participate the projects, but one student can participate several projects at the same time.
In 1st statement, the relationship of student and project is M-1. But in the 2nd statement, the relationship of student and project is 1-M
If I want to express their relationship in a single ER digram, should I use the M-1 or 1-M? Or is my ER diagram wrong?
ER Relation
I want to clarify my diagram that I have created;
ER diagram
I was wondering what I have made means the following things;
- A company can book multiples jobs
- A company MUST own a job for it to exist
Am I correct in those assumptions from my diagram or have I done something wrong?
I am an ICS student and I have been given two questions.
1.) List all the Functional Dependencies that hold for the database.
2.) For each relation in your relational schema write down whether the relation is in BCNF or 3NF and if not give a violating FD.
I'm just having problems understanding the relationship between functional dependencies and the ER Diagram. I've watched a few videos online but I'm still getting stuck on how to answer the two above questions and would appreciate some help in finding the right direction.
Below is an ER diagram and I was hoping someone could give some examples on how to start from here.
For each entity set (e.g. Department), each attribute is an FD (e.g. Department Name -> Location).
For each relationship set (e.g. Offers), there's an FD from the combination of keys of "many" entities to each of the keys of "one" entities (e.g. Course_ID -> Department Name)
In some ER diagrams there are attributes on the relation.In what occasions should we use attributes on the relation
Attributes on relationships allow you to record facts about the relationship as opposed to one of the entities that make up the relationship. Some examples:
A marriage between two people has a date and venue
A student's class allocation may have an assigned seat
Popularity ratings by customers on products
Here's an ER example of an attribute on a relationship between student and class:
While the semantics of ER seem familiar and aid its popularity, logically the distinction between entities and relationships is artificial and unnecessary. Entities can have composite keys, and unary relations aren't unusual from an n-ary relational point of view.
Using Chen's notation on an entity relationship model, for database design. Is this the correct way to illustrate the following relation. 'Many employees report to one employee':
I think the below image would be more approapraiate
E-R Diagrams
DATA MODEL
STACK SIMILAR QUESTION
You dont need the diamond. You can have the direct relationship. Unless the relationship itself has attributes, the diamond is not used.